BOSTON (CBS) –  Wednesday could have started a few days of rest for the Boston Celtics, awaiting their Eastern Conference semifinal against the Chicago Bulls or Philadelphia 76ers.

Instead, they now have to prepare for a Game 6 against the Atlanta Hawks at the Garden on Thursday night.

The Celtics couldn’t shake the pesky Hawks in Tuesday night’s 87-86 Game 5 loss in Atlanta, despite having chances in the end. It took a Celtics flurry — a 7-0 run– late in the fourth to pull even at 83, and then a clutch three-pointer by Paul Pierce with 50 ticks remaining to pull within one, but then it just kind of fell apart.

“We played in spurts, and that’s why we lost,” head coach Doc Rivers said after the game.

From a poorly executed foul to Rajon Rondo’s final… attempt, mental mishaps cost the Celtics a chance at winning the game, clinching the series, and locking up some R&R time before the next round.

It started with Pierce missing a jumper with 18.9 seconds remaining. Pierce, showing signs that his ailing knee could be worse than thought, missed badly and the ball barely hit rim, bouncing out-of-bounds to give the Hawks the ball back with an 87-86 lead. But instead of fouling right away, the Celtics let eight seconds flow off the clock.

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Rivers said the team opted to go for the steal, but the problem was Boston still had a foul to give. Precious seconds fell off the clock as the Celtics ran around, hoping they could jar the ball loose, or into the hands of a poor free throw shooter.

“We signaled to foul, but our guys decided to go for a steal first,” Rivers said after the game. “What they didn’t understand was that we had a foul to give. I told them after the game — we talk about it every night and every day in practice — end-of-the-game execution is going to win or lose playoff games for you. You think about it, that’s seven extra seconds that Rondo would have had (for a final shot attempt). That doesn’t mean we make a shot, but you never know. We would have had extra time, and we didn’t have it.”

Despite their brain fart, the Celtics still had another shot at winning the game. Rondo stole Josh Smith’s inbound pass with 10 seconds remaining, his fifth steal of the game, and sped down the court with the game-winner in mind. He was looking to go to Kevin Garnett, but got himself trapped along the sideline with Al Horford there to defend. Rondo in turn lost control of the ball and his desperation pass was knocked away by Smith, who breathed a huge sigh of relief as the game ended.

“I tried to make a play, but got caught on the baseline,” said Rondo, who tallied 13 points and 12 assists in the loss. “Give Al credit. I just didn’t come up with the shot.”

“We were in a jumble,” Rivers said. “I wish (Rondo) had went down the middle of the floor, I think you should always go down the middle of the floor, especially when have a big on you. Listen, it’s a turnover, it’s a fast break — we were just trying to go. I thought Kevin set a nice step-up pick; I was hoping he would attack the basket. But really, I just thought he lost the ball and that threw off any chance we had.”

“They defended it pretty well. (Rondo) came off the pick-and-roll, they switched and then cut off the baseline. At the end of the day, he gave us a chance,” said Paul Pierce, who along with Garnett led the way for Boston with 16 points apiece. “We were put in a situation where we were probably going to have to foul and maybe go down 3, but he got the steal, gave us an opportunity. Unfortunately, we turned it over. Sometimes it goes like that.”

“We definitely squandered away an opportunity today, but you take your hats off to the Hawks, they came with a purpose,” added Pierce. “It’s a make-or-miss league, we had our opportunities down the stretch, they played with a lot of energy, a lot of pride with their backs against the wall and won a close one.”

So the Celtics squandered a golden opportunity to rest up in advance of a potential second round appearance. Chances are they will close out the series on Thursday at the Garden, but with Philadelphia losing their Game 5 chance at sending the Bulls home for the summer, the Celtics missed out on a great chance to rest up their injured players while their next opponent had, at least, one more game to play.

Instead of some rest and relaxation, the elders in green have to worry about at least one more game with these pesky Hawks.