Each appeared from nowhere, a pair of meteors nobody saw coming suddenly bursting into view, threatening to knock us out with surprise. Knicks vs. Celtics. Rockets vs. Thunder. Two runaway first-round playoff series, now caught in a state of suspense. From "sweep" to six games.

And maybe a Game 7.

And possibly … history in the making?

No team has ever won a best-of-seven playoff series after trailing 3-0, or depending on how you choose to look at it, choked away a series after leading 3-0. It'll happen eventually. At some point, a series with a lopsided start will be shaken up by injuries and drama and a turning point. Then the NBA will have its first complete reversal of fortune.

The Celtics and Rockets, down 3-2 but holding the next game on their courts, will try to pull off the unexpected Friday and Sunday. The Celtics are a seven-seed, the Rockets an eight-seed, but they're in the same pod. Both are facing teams that entered the postseason on a hot streak and riding franchise players, Carmelo Anthony and Kevin Durant, who finished 1-2 in scoring. Raise your hand if you gave them a chance after they fell behind 3-0. Uh-uh, thought so.

"We're just going to stay calm and keep climbing the mountain," Paul Pierce said. "We didn't get down when we fell behind and we're not going to get too `up' right now. We'll just play the next game like our season depends on it, because it does."

Here's what happened and where it might go.

Knicks-Celtics

How they got here: Celtic Pride tends to be a bit overstated at times, but this isn't one of them. Yes, Pierce and KG are old and cranky. True, the young supporting cast is mostly in way over their heads. Absolutely, after an uneven season, the Celtics are lucky they're in the East or they wouldn't be here. But when you back them into a corner and try to embarrass them, you're taking your chances. The Knicks weren't content to take a 3-0 series lead. They had to swing an elbow, dress for a funeral and talk a lot of mess. That, along with some blue-collar play from KG and Pierce, is why this is going to a Game 6.

Series changing moment: The cheap-shot elbow swung by J.R. Smith in Game 3 blew up in his face, not Jason Terry's. With Smith suspended for the next game, Melo felt pressured to shoot 35 times, many of them forced. And the Knicks still had a chance in the fourth quarter to sweep the Celtics. So that loss was on Smith. And the fallout from that was seized upon by Boston. The elbow swing, coupled with the Game 4 win, seemed to energize the Celtics. Smith did himself and the Knicks no favors by coming up weak (three-for-14 shooting) in Game 5, and now here they are, locked in a tighter series than they expected just days ago. Oh, we should add it was Kenyon Martin's idea to dress in funeral black before that game. Now you know why Smith, despite winning the Sixth Man of the Year award, and Martin, a valuable late-season pickup that nobody wanted, will always be risks.

Drama: It's not that players back in the day didn't talk about your mama or your wife or girl; on a hunch, the language of the Oakland Raiders in the 1970s was probably rated NC-17. The difference now is we have a million camera angles and professional lip readers and social media. And also some very sensitive players who just can't let it slide. Therefore, the Knicks and Celtics are linked, right or wrong, fairly or not, by LaLa Anthony, target of Garnett and now Jordan Crawford. Only in this series are reporters staking out the team bus, just in case.

Developing hero: Raymond Felton is having a terrific series, causing absolutely no one to miss Jeremy Lin. He's averaging 18.4 points, which is almost five full points over his season average, with almost seven assists a game. A year ago Felton was an out-of-shape castoff from the Blazers. And now, what would the Knicks do without him, especially with Jason Kidd finally showing some age? We should point out that Felton is padding his stats and performance against Avery Bradley and not Rajon Rondo. There is, um, a difference. Big.

Developing goat: This is a pretty tight contest between Terry, who has rallied after a dreadful start (4-for-18 shooting in the first two games) and Bradley (out of sync at point guard) and the Carmelo of the last two games (18-for-59 shooting). But Smith is really the reason the Knicks haven't finished off the Celtics, and unless he gets his head and his stroke right, there could be a Game 7 and maybe even a long, hot and bitter summer in the Big City. At least he's not sweating: "If I miss five or six shots, the next seven or eight (are) going up, anyway," he said.

Where it's going: The Knicks had a pair of sub-par shooting nights in Games 4 and 5, one without the league's Sixth Man of the Year. Plus, they'll be without an injured Steve Novak in Game 6, while Melo has a sore shoulder. That said, the Knicks are in better shape than the healthy supporting cast for KG and Pierce. The Celtics made a nice stand that deserves applause, and Doc Rivers won't allow them to quit. But once the shots fall again for the Knicks, so will Boston, either Friday or Sunday. "I feel pretty good about it," said Knicks coach Mike Woodson, "and our guys do, too."

Rockets-Thunder

How they got here: Oklahoma City blasted the Rockets in Game 1 by 19 points. The next four were decided by 15 points. Obviously, the Russell Westbrook injury in Game 2 was a blow. And the Thunder would've swept had Serge Ibaka not short-armed a point-blank layup at the buzzer. But the Rockets, youngest team in basketball, have shown some surprising poise in frantic moments. James Harden shot well only in Game 5. Otherwise, he's getting to the free-throw line and also bailed out by a few teammates, including Chandler Parsons, who dropped deadly three-pointers in Game 4. From a talent standpoint Houston still doesn't compare, even without Westbrook. And yet in the first taste of real playoff pressure in his life, Kevin Martin is shooting 30 percent and coming off a 1-for-10 stinker. Reggie Jackson is averaging 17 points since replacing Westbrook but isn't a pass-first point guard and it shows. Besides him and Durant, players are coming up small for OKC.

Series changing moment: Westbrook's knee injury deprived OKC of a strong No. 2 option and the post-game podium of some weird looking outfits. For those blaming Patrick Beverley for playing dirty, props to TNT for finding a clip from earlier this season showing Westbrook pulling same stunt on Jeremy Lin, then reacting angrily when Lin took minor offense. Anyway, OKC was in trouble after the doctor broke the bad news. What happened next was a combination of two factors: Thunder feeling deflated, Rockets feeling elated. One team was suddenly scrambling to reinvent itself because, remember, OKC had never been in this position before. Westbrook never missed a game in his NBA life (and his basketball life). Roles were changing on the fly and players were being asked to compensate for Westbrook, including Durant. Meanwhile, the other team suddenly discovered it had a chance. Which is now the case for the Rockets.

Drama: Twitter is terrific for social interaction and exchanging ideas and thoughts, at least when it's used the right way. And then there are Twitter Gangstas who hide in their home office and act tough on their keyboard. An Oklahoma City ball boy threatened Beverley's life. The kid obviously didn't know Beverley is from the West Side of Chicago. He should visit sometime. A few days later, Royce White, the anxiety-stricken Rockets rookie who didn't play a single game this season and isn't on the playoff roster, teased Durant after Game 5. White tweeted the Thunder is "looking shaaaaky baaaaby." When some followers took offense, White challenged them to say it to his face. That's what Durant is waiting for White to do. Oh, wait, White isn't on the team. Never mind.

Developing hero: Beverley is big because Lin missed the last two games with a chest injury and is questionable for the rest of the series. Even before his injury, Lin was sloppy at point guard and coach Kevin McHale gave the ball to Beverley. It's been a long and hard journey for Beverley, who couldn't stick with the Heat and had to bounce around the world before returning to the NBA in January. After signing him, the Rockets were ready to ship him to the D-League when McHale noticed how Beverley, in his first practice, out-hustled everyone on the floor. So he stayed. He's quick and fearless and averaged 15 points and seven rebounds in three of the five games.

Developing goat: OKC coach Scott Brooks had some 'splaining to do after his failed Game 5 strategy to "hack a … whatever his name is," according to Durant. At first, it seemed OK to intentionally foul a 50-percent free throw shooter. That way, you stop the clock and keep the ball away from Harden and Houston's three-point shooters. Once Omer Asik started making free throws, Brooks should've changed immediately and went back to playing ball. This was Brooks reaching for answers without Westbrook. Clearly, Durant was upset: "We were on the way back," before Hack Asik started, "and it kind of slowed the rhythm down a little bit." That was nice-guy Durant's way of calling out Brooks. Durant's body language in the final few minutes also said he wasn't thrilled about teammates who can't make shots, either. On a few trips, he passed the ball, then just stood and watched.

Where it's going: With Harden and Durant almost matching basket for basket and canceling each other out, this series will fall on the supporting casts. The Rockets are too streaky a shooting team to take seriously. So much depends on their outside shots falling because they're weak in the paint with no low-post scorer. That favors OKC and Ibaka to be the difference maker. Oklahoma City will squeeze by Houston but, without Westbrook, the end is near.