BOSTON -- Celtics coach Doc Rivers liked just about everything about the final play of Wednesday's game -- except the fact that the shot didn't go in.

Boston got the look it wanted when Tim Duncan switched onto Paul Pierce off a pick-and-roll, but Pierce's step-back jumper at the free throw line found back iron as the Spurs escaped with an 87-86 triumph at TD Garden.

"Listen, Paul Pierce taking a step-back at the [free throw line], that's not a bad option," said Rivers. "I just wish we could have done it a bit earlier."

The Celtics were down 4 with 46.5 seconds to play, but Ray Allen -- back after a six-game absence due to a sore right ankle -- hit a quick 3-pointer and Boston came up with a stop at the other end of the floor to set up a chance to win the game.

Boston didn't make particularly good use of the clock, scrambling to call a 20-second timeout with 7.9 seconds remaining after Garnett initially hauled in the Spurs' miss with 15.9 seconds to go. Even still, Boston got the ball into Pierce's hands (off a little screen from Rajon Rondo) and forced San Antonio to switch when Garnett came out to run the pick-and-roll.

Pierce, the newly minted Eastern Conference Player of the Month, had a chance to drive with a little more than 5 seconds on the clock, but seemed leery given that San Antonio had both a foul to give and Manu Ginobili was cheating toward the lane as Pierce started driving right. Pierce ultimately reset and came back to the middle of the court, getting the shot up over Duncan, but it was just a little long.

"I was trying to make the shot," said Pierce. "I got the switch on the big man, got to a good place -- I just missed the shot.”

Pressed on if he considered driving, or if he expected the Spurs to give a foul, Pierce shrugged off both notions.

"This type of stuff is not really pre-scripted, you don’t have an idea of what’s going to happen in those type of situations," said Pierce. "You get in those pressure situations and sometimes they work and sometimes they don’t, but the thing is I’m not going to second-guess my decision. I thought I got a great shot, created some space right there at the free throw line. It's just some days they fall, some days they don’t."

Rivers only found fault in waiting to take the shot. Given that the Celtics were trailing, he would have liked to have at least given the team a chance to get a tip-in (Avery Bradley came crashing hard from the baseline as Pierce misfired), but the coach found little fault otherwise.

"We actually said that they probably would [give the foul] and we were trying to get Duncan on a Paul matchup, because we thought we had the speed advantage," said Rivers. "We wanted him to go a little quicker because I thought [Pierce] could’ve beat [Duncan] off the dribble and he would’ve reached the foul line and you know Paul has a knack of getting the ball up. But his step-back is what he wants. I just thought we waited a little too late in the clock.”