The San Antonio Spurs did nothing but win for one month and 20 days. They became everybody’s favorite to win the NBA title. J.A. Adande wrote a column saying they were likely to sweep through the entire playoffs. They looked like a juggernaut, an unbeatable concoction of spacing, skill and basketball intellect.

But 51 days after beginning a 20-game winning streak, the Spurs were dismantled by the Oklahoma City Thunder, 102-82, Thursday night in a contest that was anything but close. Zach Lowe wrote afterward that San Antonio is in danger if it can’t figure out Oklahoma City’s defensive adjustments. The Associated Press game recap began, “The streak is over. The series might only be beginning.”

In baseball they say momentum is only as great as a team’s starting pitcher. In basketball it can hinge on one half, one quarter, one coaching adjustment, one player doing more than he’s expected to (see: Brandon Bass, Philadelphia 76ers series, Game 5), one late-game stroke of luck, one star who picks the right time to behave like one. An NBA series can be flipped quicker than a pancake. A team can be down 0-2 with hardly any hope one day and level a juggernaut the next, clawing within 1-2 and surfacing questions of whether the Spurs might now be in trouble.

“We’re going home now,” Mickael Pietrus said of the Boston Celtics, another team looking to turn momentum on its head, according to the Boston Herald. “Our jerseys are going to be white. They have two — good for them. But you know what that means when we say we’re going home. We played the game we wanted to. Now we’re going to go home and try to take care of two games. I know we’re down by two, but that doesn’t mean anything.”

It does mean something. It means the Celtics are two games away from an uneasy offseason and it means they better win Games 3 and 4. It means the Celtics need to play like they did in the first half of Game 2, with aggression and defenders flying everywhere, with purposeful cuts and unselfishness abound. It means they need Kevin Garnett to play like he did in Game 1, Rajon Rondo to play like he did in Game 2 (though he almost certainly won’t duplicate the stat line, his attacking is a must), and Paul Pierce and Ray Allen to come as close as they can to matching LeBron James and Dywane Wade’s production. It means the Celtics’ bench (seven points in Game 2) can’t be so quiet and Miami’s role players (Udonis Haslem and Mario Chalmers combined for 35 points in Game 2) can’t be so loud.

“We have to understand what’s beating us right now,” said Paul Pierce, also according to the Herald. “They got the offensive rebounds, the loose balls and the kickouts for 3’s. They kicked out to Chalmers or Shane Battier for a 3, and it’s demoralizing when you play good defense for so long. We have to be able to make it one possession, rebound and get the ball out.”

The Celtics face a stiff task. They need to win four games in the next five against a Heat squad featuring two of the NBA’s top 10 players, both of whom are working in synchronization. They need to find a way to keep their bodies sprinting forward even though Allen has bone spurs in his ankle, Pierce is still suffering from a sprained MCL, Garnett played more minutes in Game 2 (45) than he ever had in a Celtics uniform, and the Celtics will be playing Friday night in their 16th playoff game in 32 days. NBA teams who go ahead 2-0 in a seven-game series win 94.3 percent of the time. The Celtics as a franchise are only 1-8 after going down 0-2 in a seven-game series, with the only win coming 43 years ago in the 1969 NBA Finals.

“Soldiers keep fighting,” said Pietrus.

“We just have to play better. We’re not going to blame (anyone) — we have to play better,” added Doc Rivers. “And we will.”