Some keys to me:
1) The step-up guy- Miami keeps having at least one player a night unexpectedly stepping up and delivering a big performance. Battier did it in Miami's first two wins, and it was Chalmer's turn last night. This is very much how OKC beat San Antonio - good play by the big three but each night a different guy would step up - Ibaka with a perfect shooting night and 26 points, Perkins with a big double-double, Sefolosha with 20. OKC is having a hard enough time getting good games out of all the of their big 3.
2) Only big 2 - Harden must be inside his own head right now because he's having about the worst stretch I've seen him have. When the game was tight he had three or four great open looks for three and he clunked them all. Unlike when Wade has an off-night shooting and compensates with steals, blocks, great D and facilitating the offense Harden just seemed to do a whole lot of nothing last night. That's not how they got here and that's not how they'll win here.
3) The complete player - One of the most athletic, fit, players in the game played himself to the point of complete physical exhaustion last night. You could see him struggling to breath mid 2nd quarter and yet he was still on the court in the 4th, when his muscles just gave out on him. You hear about 110%, but you rarely see it. While I wouldn't put this game on the level of Jordan's flu game, he did have 5 huge points after the injury in clutch time. In a way this game was his most impressive of the playoffs - two quarters of facilitating, with 12 great assists (one Ginobli-like) then when they were getting beat in the third they took a timeout, he came back in and scored aggressively like they needed him to. Scoring, rebounding, passing, defending 1-5. You can find a player in the league who's better at any one of these things - but he is the only player (without sounding melodramatic, perhaps in history) with such a potent mixture of all these elements. It is worth mentioning that Wade is possibly the most complete two - a great scorer, passer, stealer, who may also be the best blocker and rebounder for his size.
4) Rebounds- How does Miami keep out-rebounding OKC? I don't understand what Ibaka and Perk are doing out there. It isn't blocking, because the whole team had two blocks last night. It isn't scoring, as together they totaled 8 points. The only theory I have is this: Miami has arguably the best rebounding 2-guard in Wade (despite his size) and indisputably the best rebounding 3 (if you want to assign him a position) in the league with Lebron. This matters when a) they're attacking in the paint (and thus in the position for offensive boards) and b) playing others who are attacking in the paint or from 15 feet (such as Westbrook and Durant last night, when you are in position down low for the defensive board.) This gives Miami a big advantage. Bosh is also a better rebounder than people give him credit for - while Ibaka is the best in the league at timing blocks, from what I've seen this series Bosh is better at timing his rebounds.
5) Assists/balance. Lebron himself had one less assist than the entire Thunder team. This game looked to be the most balanced attack yet this series by Miami, with everyone on the starting lineup putting up solid numbers, without one player having to attack play after play with the rest of the team stagnant. Cole also supplied a big lift off the bench - 8 points might not seem like much, but when you take into account that his first 6 kickstarted Miami's comeback in the second they gain a whole new meaning.
6) Fouls/free throws - did seem slightly slanted in Miami's favor. Westbrook should have had more calls, he was attacking the hoop with contact multiple times when nothing was called. (Makes his 43 all the more impressive considering he only had 3 foul shots.) On the other end, I counted 6 real fouls on Durant - stupid, stupid fouls. I don't want to sound like a conspiracy theorist, but someone must have made the call to not get Durant in foul trouble again because time and time again the refs called Durant's fouls on his teammates. This may be an unspoken policy as I have seen it before: There was a foul committed. The other team needs free throws. The refs oblige, but keep the fouls down on the superstars. Makes sense considering that the league is ultimately a business.
7) Hustle/urgency - nowhere was this more evident than in the last five minutes with three great plays. Wade dove out of bounds twice for rebounds and got them back to his team. Only Wade. The other play that defined Miami's hustle to me was the jump ball that sealed the game. Haslem lost the tip, but Battier out-angled Durant who was in clear position to get the ball and tipped it to a teammate in the corner, who was fouled by Westbrook in his one big mistake of the game. This is not the same Miami team who played a lackluster last couple of games against the Mavs last year. I'm not certain that the addition of Battier can be quantified with currently available statistics. The defense all game was also great, with Miami closing off the lane to penetration (especially Harden,) rotating and closing out well, and not making stupid fouls. I don't think any team could have contained Westbrook last night.
Each game in this series has been tremendous as we see just what these players can do, individually and collectively. I'd like to see an extended series, but the series being 3-1 does not make it a bad series unless you are emotionally invested in OKC.