If the Celtics proceed to lose this series—and after falling behind 3-1, winning will be no small task—they will have nightmares about tonight. They will wake up with their hearts pumping, sweat dripping down their bodies, the sheets strewn across the bed. And a series of plays will be running through their heads:

Rajon Rondo’s wide open layup in the final minute. The fast break pass Rondo threw behind Jeff Green. The final possession of regulation, when Ray Allen and Kevin Garnett forgot what they were doing; Paul Pierce ended up going left even though he loves going right. The Delonte West three in overtime that would have cut the deficit to two. The missed box-out on Chris Bosh’s tip-in, which resulted from two odd cross-matchups—Garnett on Lebron and Paul Pierce on Bosh. The three-pointer Lebron hit from the wing to tie the game at 84. Dwyane Wade’s stepback, extra-long two in Delonte’s mug. The Celtics will remember all the little plays that hurt their chances, because even on a night their offense went stagnant, a win was only inches away.

Two great basketball teams met at the TD Garden tonight, two teams who compete with an edge of greatness. We saw so many special things—a Lebron-Pierce first-half duel, Rondo playing (and for a short time, at least, excelling) with a deflated arm, Wade, James and Bosh winning almost three-on-five—but in the end, as playoff basketball normally does, the game came down to who could execute better in the half-court. This was the question facing the Heat all year long; when a playoff game slowed to a halt, could they still manufacture enough offense against a set Boston defense. The answer, at least tonight, was yes.

The Heat weren’t perfect. Far from it, actually, at least offensively. Lebron occasionally dribbled off his leg; he and Wade settled for tough fadeaway jumpers; and their teammates (not including Bosh) did mostly nothing. Miami, like Boston, was alternately brilliant and bumbling, alternately stifled by a magnificent defense and unstoppable even by the finest of defensive efforts. But when the game got put into a blender, when everything slowed down and offense became a task of precision rather than grace, Miami had enough to keep the Celtics from crashing their party. The Heat offense was timely, and their defense was everywhere; a collage of long arms and nimble legs moving in unison, making good looks for Boston as difficult to find as a misplaced hair on Pat Riley’s head.

As the Heat forced bad Boston possession after bad Boston possession, my sunken heart briefly though back to Game 7 against the Los Angeles Lakers. After I vomited right there on my couch, I pushed the memory out of my head. But that was the last time a defense forced Boston to look so bad. Don’t get me wrong: at multiple times this season, Boston’s offense has looked worse than it did during the second half tonight. Yet the prior hideousness was more complacency than anything else, while tonight was just the struggles of a team desperately searching for a way to combat Miami’s youth and athleticism. And though the Celtics at least matched Miami’s effort, I would be remiss not to mention Miami’s heart. The Heat deserved to win tonight. They earned it.

After the legendary grit Boston exhibited Saturday, Celtics fans’ worst fears were realized today: the Celtics spent every dime in their pockets on Saturday and saved almost nothing for today. In two days, they aged ten years. Kevin Garnett wasn’t nearly as aggressive, nor as productive. Rajon Rondo, after briefly casting a spell over the arena, began to feel the effects of his displaced elbow. Ray Allen found difficulty getting clean looks. Shaq could only play three and a half minutes. Paul Pierce couldn’t do it all by himself. And Glen Davis, well, let’s just not talk about him.

The Celtics were running on reserve power to begin with. But somehow, despite so much conspiring against them—out-rebounded 45-28; out-shot in both percentage (44.3% to 42.9%) and quantity (79-70); playing with a one-armed point guard; relying on three stars that are a combined 102 years old; and struggling to match up with Miami’s small lineup down the stretch—the Celtics were right there on the cusp of tying the series. So many times, one play—one forced turnover, one made jumper, one rebound—could have turned the game in Boston’s favor. But the Celtics never made that play, and if they lose one more time, they’ll have the rest of the summer to regret it.