For the Celtics, the challenge in taking away any part of Paul Millsap’s game on Sunday was that a new one would then sprout. Stop his drives and he’d spot up for 3-pointers. Stop him from facing the basket and he’d score in the post.
Coach Brad Stevens tried most everything on the 6-foot-8-inch All-Star until a moment midway through the fourth quarter when he went with one final hunch that was both risky and, ultimately, prescient.
“Marcus,’’ Stevens said, “guard him.’’
Marcus Smart was surprised by the decision, particularly because he gives up 4 inches and 26 pounds to Millsap. But his aggression and toughness can mask more obvious measurables. Smart was the antidote to finally slow Millsap, who had just 2 points over the final 10 minutes after erupting for 43 prior.
Smart’s pesky defense — combined with his timely fourth-quarter scoring spree — sent the Celtics to a 104-95 overtime win over the Hawks in Game 4 of this first-round playoff series, which is now tied, 2-2.
Game 5 will be played in Atlanta on Tuesday night, and the Celtics’ win Sunday guaranteed that this increasingly dramatic matchup will at least return to Boston for Game 6.
“They responded to being down, 2-0,’’ Hawks coach Mike Budenholzer said of the Celtics, “and now we’ve got to go home and respond.’’
A few days ago, a run like this seemed improbable for the Celtics. The Hawks had torched them early in the first two games, holding on to win the first before blitzing them in the second. And to add to an already steep challenge, Avery Bradley and Kelly Olynyk were out with injuries.
But this TD Garden revival, buoyed by a frothing, lively crowd that included Patriots coach Bill Belichick and tight end Rob Gronkowski, has turned this into anyone’s series again.
“We just tell each other, ‘This is what we work all year for,’?’’ Smart said. “?‘This is what we bled for, we sweated for, the tears, for a moment like this to go out and play in front of a crowd like tonight, and give it all you’ve got.’?’’
Point guard Isaiah Thomas finished with 28 points and six assists to lead the Celtics. Smart, who played the game’s final 26 minutes, finished with 20 points, 8 rebounds, and 5 assists, and his defense of Millsap might have been more essential than all of that.
“You give Marcus Smart an assignment, he’s probably going to get it done, no matter who he is playing against,’’ Thomas said. “He’s a hell of a competitor.’’
The Hawks led at the start of the second half, 48-46, when Millsap seized control with three baskets during a 14-0 blitz that made it 62-46. Suddenly, the Celtics were reeling.
But late in the third quarter and early in the fourth, the Celtics unfurled a 12-0 run that included four baskets — and two 3-pointers — by Jonas Jerebko. His spinning layup that capped the surge gave the Celtics a 74-73 lead.
Rookie Terry Rozier replaced Thomas to start the fourth quarter, and Thomas generally sits for about six minutes around that time. But in this game, clearly, that was not an option. Once Atlanta went on a quick 7-0 run to take an 80-74 lead, Thomas was back. That is also around the time Smart switched onto Millsap, as he pestered him aggressively each time he caught the ball.
“My teammates were very supportive about that, just telling me, ‘You can guard him. Just stay down and force him into our help, and just play with your hands back,’?’’ said Smart.
Smart took over on offense, too. Over a four-minute stretch he made a layup as he was fouled, drove the left baseline and threw down an aggressive dunk, and then drained consecutive 3-pointers, the second giving the Celtics an 85-84 edge.
The Celtics led by 4 points until Jeff Teague hit a 3-pointer from the left arc with 49.7 seconds left and another with 20.2 seconds left, giving the Hawks a 92-90 lead.
After a timeout, a layup by Thomas tied the score at 92. Teague then held the ball as the clock wound down and lost control as he went up for a jumper with less than a second left, sending the game to overtime. It was a sloppy, awkward play that came after consecutive Hawks timeouts. Budenholzer said Atlanta was focused on not giving Boston another shot.
“I don’t know what they were doing,’’ Thomas said. “I think they were trying to isolate me. I felt like he took a little bit too long and I kind of knew what he was going to do once the clock hit three or four seconds.’’
The Celtics led, 97-95, in OT when Kent Bazemore appeared to give Atlanta the lead with a three. But the review showed that he did not release the ball before the shot clock expired.
At the other end, Evan Turner hit a baseline jumper to put the Celtics ahead, 99-95, with 1:34 remaining. After missed jumpers by Kyle Korver and Teague, Thomas drilled a 3-pointer from the right corner with 30 seconds left, giving the Celtics a 7-point lead that would not be touched.
Adam Himmelsbach can be reached at adam.himmelsbach@ globe.com.
