Ray Allen returned to the court after missing six games with a sprained ankle and was in the starting lineup as usual on Wednesday when the Celtics played the Spurs. The debate over whether he or Avery Bradley should start has been a constant talking point over the last three days, but it was the second part of that question -- who should come off the bench -- that was just as crucial.

On the one hand, it was argued, Allen’s scoring ability would be a welcome offensive jolt to a second unit that has struggled mightily to score points. But in the NBA, versatility is a trait that is most valued in bench performers and in Bradley, the Celtics suddenly find themselves with a defender of uncommon ability – a mini version of Tony Allen, if you will. Replacing Ray Allen in the starting lineup would have been a major shakeup, but by plugging Bradley into the sixth man role, suddenly the Celtics have options.

Bradley played 34 minutes, more than anyone in a Boston uniform except for Rajon Rondo, Paul Pierce and Allen. He was often used in smaller lineups with Rondo, Allen, Pierce and either Garnett or Brandon Bass, and he was on the court for the final 18 minutes of the game.

“It’s what I tried to tell you guys before the game,” Doc Rivers said. “Start him or not, he’s going to play the same. He was terrific. The small lineup saved us tonight.”

Almost saved them, anyway. The Celtics lost 87-86, snapping their five-game winning streak. It would have been a good game for them to win with the Bulls looming on Thursday and then a back-to-back with the Pacers and Sixers this weekend.

They lost because they failed to execute down the stretch and the Spurs made a handful of big plays while they did not. They lost because they missed seven of their 13 free throws and because they gave up 59 points in the first half.

The other way to look at it is they almost won despite those factors and Bradley’s role in the comeback was immense. He scored a game-high 19 points on 9-for-16 shooting. His defense was once again superb, this time limiting Manu Ginobli to just five points on six shots.

“He’s a pain in the ass,” Spurs coach Gregg Popovich said. “I mean, the game starts and you know what he’s going to do. He’s going to cut from the corner to the bucket and lay it in. He’s going to cut diagonally from the top. You’ve got to give him credit. He knows his role and he does it very, very well. He killed us all night long.”

Bradley continues to be a revelation, but let’s be clear: His play is no longer a surprise. He’s scored 92 points over the last six games and is shooting 54 percent. That’s not a fluke and it’s more than a trend.

“He’s been playing like that for the last six or seven games,” Rondo said. “It’s kind of what we’re expecting from him. He’s playing big and that’s what we need.”

For years the Celtics have been one of the most traditional teams in the league. Their one minor concession to versatility in their lineups was using first James Posey and later Glen Davis as a four/five man with the other four starters. They have been slowly morphing into a more versatile team.

This transition began with the move of Garnett to center, but it was gaining traction with Mickael Pietrus as a Posey-like hybrid. Now it’s Bradley who allows Rivers to play unconventional lineups.

“In stretches it changes up the game,” Keyon Dooling said. “We’re able to get out do some different things in pick and roll defense, and also able to exploit the matchups offensively. With the playoffs approaching there will be a lot of different lineups, so small ball is pretty good. In the playoffs you have to have versatile lineups. The more flexible you are in your rotation the more equipped you are to compete against anybody.”

The Celtics had to go small against the Spurs because their second unit sliced them to ribbons in the second half thanks to Matt Bonner who stretched the floor with his 3-point shooting ability and Gary Neal, who knocked down shots off the pick and roll.

“When they put a range-shooting three out there, they’re so tough to guard in the pick and roll,” Pierce said. “It allows us to switch so we didn’t leave Bonner open, we didn’t leave Gary Neal open in the second half. We have that ability to do that with the players we have. We don’t do it a lot. In this case, with the way San Antonio plays it was successful for the most part.”

Switching is anathema to the Celtics’ defensive philosophies. It’s an out for the weak-willed, for those players who don’t feel like fighting through screens. But on a team with the right defensive mindset, switching defenders can be an attacking strategy instead of a passive one. 

In order to switch and do it effectively, you have to have players who can guard multiple positions and in Bradley, Rondo, Pierce and Garnett they have four players who can handle the assignment. Pietrus, meanwhile, may be the key to the postseason. If he can return from his severe concussion, then suddenly the Celtics become an even more devastating defensive squad.

“That’s something we have not had,” Rivers said after Sunday’s game with the Heat. “We’re switching things that we would never switch.”

Whether he starts or comes off the bench, Bradley has become more than just a rotation player. He’s now the sixth man, hallowed ground for the Celtics. It’s a position that demands versatility and ability to impact the game immediately. It may just be a perfect role for him.