The Boston Celtics trailed 28-20 early in the second quarter when Kevin Garnett caught the ball in the low post. The Atlanta Hawks had scored the game’s previous nine points and threatened to break Game 6 wide open. Garnett, at that point, had sunk just one of his first five field goal attempts. But his slow start would lead to one of his most memorable performances with the Boston Celtics.

From where did he draw his inspiration? Garnett would later thank Hawks co-owner Michael Gearon Jr. for calling him the league’s dirtiest player, saying Gearon only provided him with more motivation. No. 5 also sent his gratitude to all the columnists and reporters who called him old, or who seemed to be surprised by his three-month string of incredible basketball that started sometime around the All-Star Break. Even after his comments, it’s difficult to imagine Garnett demanding the ball in the low post while thinking to himself, “This is for you, Gearon” or “I’m scoring this for you asshole columnists.” The Celtics had a playoff game to win, and I imagine that’s what rested on Garnett’s mind when he sealed for position on the low block.

He probably didn’t need much in the way of outside motivation. This was the NBA playoffs, after all. Garnett has always been obsessed with winning, so much so that he once famously broke down crying during an interview with John Thompson. The Celtics needed to win Game 6 or else fly down to Atlanta for a Game 7 on the road. Down eight points in the second quarter, the game, the series lead and even maybe the season were all slipping away from them.

Garnett hit an and-one to cut the deficit to five. This is what the Celtics had long been waiting for, what Garnett’s loudest critics once claimed he couldn’t, or — maybe even worse — wouldn’t, do. This was Garnett demanding the basketball on the block, using his array of low-post maneuvers to score regardless of who defended him. This was Garnett, after starting the game by missing several good looks, having the steely grit to continue parking his keister as close to the rim as possible and keep calling for the ball.

What motivates Kevin Garnett? Yes, people who call him old and the Atlanta Hawks’ owner and a number of other detractors who complain about his intensity or occasional elbows or the fierce way he plays basketball. But those sources provide nothing more than temporary fuel. As Garnett noted last night, he’s been this dedicated since he entered the NBA in 1995, long before Gearon owned a portion of the Hawks or many of the reporters calling Garnett old were writing about the Boston Celtics. Many years before he sat on the podium and thanked his new sources of energy, Garnett built a more permanent foundation on which he would build his success.

Respecting the game of basketball became the bottom of Garnett’s pyramid, its base, which meant he always needed to keep himself in top shape, which meant he would wake up at 5 a.m. to run several miles on the sand in Malibu Beach during his summers. Respecting the game meant respecting his teammates, which meant he would sometimes spend up to an hour after practice to go over Boston’s defensive schemes with relative nobodies like Ryan Hollins. Sometimes Garnett’s teammates were not receptive to his advice. Rather than keep trying or moving on with a smile, Garnett would completely cut off all communication. That might seem harsh, but it all comes back to that r-word — respect. If you aren’t willing to listen to a 14-time NBA All-Star, Garnett believes, you don’t treat basketball with the care it deserves.

At halftime Rivers told Garnett to stop being a ball mover. Garnett has always put his team’s success above his own, sometimes to a fault. When he senses that the team is stagnant, he will often pass up an open jumper just to swing the basketball and encourage more crisp offense. Sometimes that’s what the Celtics need. But in a potential series-clincher, in a low-scoring series during which Garnett repeatedly showed the ability to carve out prime real estate close to the basket, the Celtics didn’t need Garnett to politely swing the ball to his teammates. They needed him to shoulder the scoring, to become a killer. The lack of a killer instinct has always been what haters highlight to disparage Garnett. Even when he made the right pass early in his career to a wide open teammate, critics would say he should have been more selfish.

There was nothing selfish about the way Garnett controlled last night’s game — he scored 28 points on 19 shots, all of them good looks, drew 10 free throw attempts, covered for his teammates defensively whenever he was needed, blocked five shots, notched three steals, and generally did what he does, which is to be in the right position and make intelligent plays — but perhaps he competed with an extra force, with the knowledge that the Celtics, with Ray Allen and Paul Pierce hurting, needed his offense then more than ever. When people call for The Big Ticket to be more selfish, last night is what they want. They don’t want him to freeze out teammates or force bad shots. They just want him to realize what an unstoppable force he can be, with his length and skill and soft touch and knowledge of the game.

Garnett shouldn’t be this unstoppable, not anymore, not on both ends of the court, not on a consistent, nightly basis like he has been ever since the Celtics returned from the All-Star break, ever since the first All-Star break in 13 years that didn’t see Garnett represent his conference. He chastised reporters for calling him old, but in reality Garnett is old. At 35 years of age and three years removed from serious knee surgery, with almost 46,000 regular season minutes played, Garnett is well past the point in his career where most athletes break down. Hell, even he broke down three years ago and dragged his body around for most of the 2009-10 season. We didn’t have any evidence — not from Garnett’s recent past, not from other big men in NBA history Garnett’s age with as many miles on the odometer as Garnett has — that he could still be this good, this dominant.

With 6:33 remaining last night, Garnett asked for a sub. He was tired and spent, perhaps the night’s lone admission that Garnett isn’t what he used to be. He had used everything he had to control the Hawks, and he left with a 74-65 lead. What followed was an unraveling that wasn’t atypical when Garnett left the court during the series. He returned after a timeout less than two minutes later. Boston’s nine-point lead was now one, 76-75.

“I don’t know exactly what the plus-minus number is, but if you look at Kevin’s plus-minus in this series — when he’s on the floor and off the floor — it’s really tough to take him off the floor,” said Rivers of Garnett, who’s presence on the court, according to Basketball Value, made the Celtics 52.77 points per 100 possessions better through Game 5. That’s insane. “In the playoffs, I think he leads the league. It’s crazy, his numbers. And it’s also crazy, other guys’ numbers when he’s on the floor.”

I once thought a thirst for winning consumes Garnett, and perhaps it did or maybe does, but now I think he’s just as happy with the process of trying to build a winner. He loves having young teammates willing to do what it takes to learn. He loves having veteran teammates committed entirely to winning and nothing else. He loves being a part of the Boston Celtics, a team that never has any drama over shot attempts or minutes played. He wants to win a title, sure, but he’s come to realize that only one team raises a banner every year, and that other teams can still be proud of their accomplishments. Championships are still the goal, but Garnett now seems to measure what he and his teammates put into the game as much as what they get out of it.

Basketball is a complex sport, and Garnett understands that better than almost everyone. Whereas baseball amounts to one batter attempting to hit off one pitcher, with very few outside influences determining what type of contact the hitter makes, basketball is a game far more difficult to measure and to explain. The positioning of one offensive player on the court can impact how easily another scores. Scoring efficiently is about talent, yes, but it’s also about floor spacing and executing sets and a number of other variables that can be difficult to finger, but matter.

“This game is a rhythm game,” Garnett explained. “It’s a chemistry game. You just don’t get that through the first two weeks, three weeks, first month of the season. As you gradually go, you get better. I believe that, and that’s all predicated to the work ethic which you put into it.”

The Celtics trailed by one point before Garnett made the go-ahead shot with 30 seconds left. Doc Rivers would later describe how impressive it was that the Celtics even found Garnett, and he didn’t mention how improbable it was that they even arrived at the possession — Ryan Hollins, released by the Cavaliers six weeks ago, not a part of the Celtics’ rotation six days ago and notoriously one of the NBA’s worst rebounding big men, seized an offensive rebound in traffic.

The Celtics then ran an intricate set in which Garnett was the final option. First Pierce came off a curl screen, and he was open for a split second. Rondo might not have considered Pierce open enough to feed, or perhaps Boston’s point guard noted in his head that this was Garnett’s night and wanted the play run all the way through for KG. Ray Allen came off two screens to the corner next. Atlanta, knowing Allen’s history, doubled him on the catch. Ray Allen wouldn’t beat them — not without four hands in his face, at least.

But Allen made a nice pass inside to Garnett, who by that point was single-covered in the paint. The Celtics would have botched the play earlier in the season, when they were 15-17 in their first 32 games. But it’ a rhythm game, it’s a chemistry game. As you gradually go, you get better. And so the Celtics ran the play seamlessly, even against a strong defense playing with the intensity of a team that would go home if it couldn’t get this one stop. Garnett caught the ball isolated in the post. He might have looked to pass on another night. But on May 10, 2012, he was not looking to give up the rock. His shot fell, Al Horford missed a free throw and the Celtics advanced.

Nobody knows how many more years Garnett will play. He hinted during his press conference that he’s thought about retiring after this season. Nobody knows how man more wins the Celtics will accumulate. Nobody knows how many more nights the Big Three will call each other teammates. This year seems like the end of an era.

But no matter how this ends, no matter when it ends, Celtics fans will always be able to look back to the night when a 35-year old Garnett kept time standing still while he added a wrinkle of aggression to his game.

Championships are great and winning is always the goal, but the process — the process is what makes it all worth it.