MIAMI -- The mission was simple for the Miami Heat. Stay healthy, and build momentum for the postseason.
They failed on both counts.
Al Jefferson hit a turnaround jump hook with one-tenth of a second to play for the deciding score, Delonte West scored 28 points for his second-biggest output of the season, and the Boston Celtics beat the Heat 91-89 on Monday night in the next-to-last regular season game for both teams.
"It's big, especially for our younger players," West said. "These last couple games have been going down to the wire. Anytime you can get that kind of experience it can only help you. It's good for our confidence after the season we've had to end on a positive note."
Jefferson finished with 20 points and 13 rebounds and Rajon Rondo added 17 for the Celtics -- but Rondo's night, at least from a Heat perspective, will be best remembered by his collision with James Posey with 5:44 left before halftime.
Posey sprained his left wrist and shoulder on the play, had big ice packs strapped to those areas postgame, and doesn't know how long he'll be sidelined.
"It's pretty much day to day for the most part," said Posey, who underwent X-rays and said further tests are still a possibility. "See how it feels."
Heat coach Pat Riley said Posey probably will miss Wednesday's finale at Orlando, but added "he'll be ready for the playoffs."
"When Posey went down, nightmares began to flash in my brain," Riley said. "We've just got to get ourselves healthy and ready. That's all this is about now."
Jason Williams hit his first five 3-point tries -- he finished 5-for-6 -- and scored 16 points for Miami, as did Jason Kapono. Shaquille O'Neal added 14 points and Michael Doleac scored 10 for the Heat, who went with some unusual lineups in an effort to rest key players before the playoffs.
Dwyane Wade had eight points on 3-for-7 shooting in 23 minutes for Miami, which is already sounding like its in playoff mode.
"We will be ready. ... It's money time," O'Neal said.
Miami gave the members of its regular rotation fewer minutes than usual. All five starters played between 23-25 minutes, and Riley was deep into the bench by the time the first quarter ended. It was a night where the little-used likes of Doleac, Chris Quinn -- who had a career-best nine assists -- and Earl Barron got plenty of play.
"I thought the second unit did a lot of good things," Riley said. "Didn't get much out of the first unit at all, but it's almost expected right now."
Miami finished its home schedule 27-14; Boston was 12-29 on the road this season, matching last year's mark.
Standings-wise, the game was irrelevant. Miami will finish as the Eastern Conference's fourth seed and will be in either Cleveland or Chicago when the playoffs open this weekend. Boston will finish with the worst record in the East and the second worst -- ahead of only Memphis -- in the NBA.
But the Celtics, namely coach Doc Rivers, still showed plenty of fire.
Rivers picked up a technical foul midway through the third quarter for arguing a three-second call against Jefferson, and his team responded with a 26-9 run over the next 9 minutes. Ryan Gomes' 3-pointer from in front of the Heat bench capped the burst, and Rivers punctuated it with a fist pump as the Celtics took a 75-67 lead.
"We've got a bunch of guys with an average age of 22," Rivers said. "Any win you can get for them is good."
The Heat battled back, taking the lead on Doleac's putback with 1:17 left, but that would be their last score. West's jumper tied it at 89 with 55.2 seconds left before Jefferson delivered the winner.
"I had hit my last two shots," Jefferson said, "so I knew if I got the ball I was going to make something good happen."
Boston hosts Detroit on Wednesday in its finale. ... Udonis Haslem and Alonzo Mourning were inactive for the Heat, as was guard Gary Payton -- who is recovering quickly from a torn calf muscle and is practicing again. Meanwhile, the injury-ravaged Celtics dressed only nine players. ... The 6-foot-1 Rondo didn't win a jump ball with 2:08 left. Granted, his Heat foe was Barron, a 7-footer.