Some numbers...
Miami scored 40 pts in the second half after putting up 54 in the first half. Of those 40 second half points 21 was scored in the 4th quarter, meaning that they only scored 19 in the 3rd. OKC on the other hand scored 58 second half points, including 27 in the third. OKC didn't take it's first lead until Westbrook's 3-point play with :16 secs left in the quarter... to put them up 74-73. OKC then outscored the heat by 10 pts (31-21) in the 4th to seal the game. While Miami was putting up those 21 points, Durant was scoring 17 by himself.
That in a nutshell tells the story of OKC's resilience in bouncing back from a slow start, and Miami's struggles after a good early start. Perhaps too it's an indictment of Spoelstra's coaching. While I think he's an easy target for haters, and that the whole "Big 3" and "not 1, not 2..." hype machine (combined with the oversized presence of Riley) sets him up for failure, I think he has reasonably opened up himself to criticism as well.
For instance, why did he start the game with Bosh on the bench, opting instead for Shane Battier (who in fairness, shot the ball very well early) and ending up with James guarding Perkins in the post. Better play-calling from OKC would have seen him end up in foul trouble early, but they didn't and lived to tell the tale. Then there's the fact that he played a largely six-man rotation with Bosh coming off the bench and Miller and Anthony playing a total of 12 mins. No explanation as to why he didn't go deeper... but one has to wonder whether fatigue (especially after a long layoff) played a factor for the starters... they tailed off to precipitously in the second half for there not to be some sorta explanation.
Without going on too much... compare that to the contribution from the OKC bench... Fisher in particular. Not huge numbers, but he's a calming presence for a young team when on the floor. And then there's Harden... of which enough has been said, but despite a sub-par game, made all the right passes and took his turn defending Wade and James. Then finally, one of the most underrated players this post-season in Nick Collison. Not only does he bang when needed, but he has a keen sense for spacing, making himself available in the paint for pocket passes leading to easy lay ups. He's also a very good rebounder... just a quality player.
Miami will bounce back... too much talent among their star players. What tonight demonstrates though is that OKC are for real... for those still harboring doubts. We've seen a young team grow up before our eyes this season, and now we are front seat witnesses to them elevating their game on the fly, setting the table for a thrilling series.