The Oklahoma City Thunder could really, really come to regret the way they spent the final 24 seconds of Tuesday night’s game.

After a pair of free throws by reigning NBA Most Valuable Player Russell Westbrook, the Thunder held a 98-92 lead over the super-short-handed Boston Celtics at TD Garden in Boston. They just needed to hang on to a six-point edge for the duration of one shot clock, make their free throws, and exit Massachusetts with their seventh straight win.

And yet!

After a driving layup by rookie Jayson Tatum to cut the deficit to four, the Celtics quickly fouled, putting Westbrook on the line for two free throws. He split his pair, giving OKC a 99-94 edge. The Celtics came right back and got a 3-pointer from point guard Terry Rozier, who continues to start on the ball for Boston in the absence of injured All-Star Kyrie Irving, to draw within one basket at 99-97 with 12 ticks to go.

Carmelo Anthony got the ball on the ensuing inbounds play, and the Celtics fouled the Thunder forward with eight seconds remaining in regulation. Again: just make your free throws, it’s a two-possession game, and you’re probably good to go. Instead, Anthony clanged ’em both, giving Boston the ball back with a chance to tie or win.

They opted for the latter, thanks:

Tatum drove left around the defense of Corey Brewer, fended off a help-side swipe from Westbrook, and got into the middle of the paint. All five Thunder defenders were within two steps of the rookie as he elevated … and pitched the ball out to Marcus Morris, planted at the 3-point arc on the right wing.

Morris offered a quick pump-fake to discard the contest of Paul George, took one dribble and lofted a long ball with just under three seconds to go. It splashed through the net with 1.2 on the clock, giving the Celtics a one-point lead that sent the Garden crowd into hysterics and left the Thunder gasping for air.

Needing a quick-hitter to get back on the right side of the ledger, the Thunder … got the ball to Westbrook, a 29 percent 3-point shooter this season, running away from the hoop, for a 3-point try. It missed off the front rim. Celtics win, 100-99.

For the Celtics, it’s an improbable pleasant-surprise of a win against a playoff-caliber opponent, one coming without four key members of their rotation — Irving, Marcus Smart, Jaylen Brown and Daniel Theis — and on the strength of some big performances from the rest of the roster.

Tatum turned in another dynamic outing as the Celtics’ de facto top playmaker, scoring a team-high 23 points on 8-for-12 shooting with 11 rebounds, four assists, a steal, a block and just one turnover in 35 minutes of work. After seeming to hit the rookie wall a bit after the new year, the 20-year-old has rediscovered his fine form of late, averaging 14 points on 48/44/81 shooting splits since the All-Star break, and marrying steady production with enough eye-popping individual plays to make even confirmed superstars take notice:

Greg Monroe (17 points, six rebounds, three assists, a steal and a block in 22 minutes) and Shane Larkin (13 points, our rebounds in 25 minutes) chipped in off the bench for the ailing C’s. Morris added 21 points on 8-for-13 shooting, and very calmly drilled the dagger.

“JT did a great job of driving, you know, committing the defense,” Morris told TNT’s Caron Butler on the court after the game. “PG flew out, gave him a pump fake, stepped to the side. All she wrote, after that […] They coming in with they full squad, and they thought it was going to be a cakewalk. We’ve got other guys over here that’s ready to compete, ready to get down, and pulled out the win.”

For the Thunder, though … I mean, woof.

After 43 pretty sluggish minutes on both sides, Oklahoma City looked poised to win this one thanks to five good fourth-quarter minutes from Westbrook (27 points on 9-for-21 shooting, eight rebounds, seven assists), George (24 points, 13 rebounds) and Anthony (13 points, five rebounds, three assists). But those dismal 24 seconds dropped OKC 2 1/2 games back of the Portland Trail Blazers in the race for third in the Western Conference. (Temporarily, at least, as the red-hot Blazers were set to take on the No. 1-seeded Houston Rockets shortly after the conclusion of Celtics-Thunder.)

“We had the game won,” Anthony said after the game, according to Royce Young of ESPN. “Up two on the road, seven seconds left, having a chance to be sealed. So, the game was won.”

The disastrous finish also put the Thunder just one game up on the New Orleans Pelicans (winners on Tuesday) and San Antonio Spurs (idle after winning on Monday) in the chase for home-court advantage in the opening round of the playoffs, and left them only two games ahead of the eighth-place Utah Jazz, who slipped behind the victorious Minnesota Timberwolves by virtue of losing to the lowly Atlanta Hawks.

In a Western playoff field so tightly bunched, and with so little time left in the season, every game matters. The Thunder had a golden opportunity to gain ground on Portland and give themselves a bit of breathing room in the battle for home-court advantage … only to squander it, falling to a team playing without three of its best players, thanks to late-game defensive laxity and missed free throws. That has to hurt pretty bad right now. Whether it hurts even worse when playoff matchups get finalized come the end of the season remains to be seen.

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Dan Devine is a writer and editor for Yahoo Sports. Have a tip? Email him at devine@oath.com or follow him on Twitter!

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