BOSTON -- Marcus Smart figures it was about the time that Paul Millsap scored his 40th point of the night, but really, it's all a blur.

Boston Celtics coach Brad Stevens, having unsuccessfully dispatched all of his big men to slow Millsap during Sunday's Game 4 of an Eastern Conference first-round series, looked at the 6-foot-4 Smart during a timeout with about nine minutes remaining in the fourth quarter and tasked him with guarding the 6-8 Millsap, who had already produced the most points in an Atlanta Hawks playoff game in nearly three decades.

"Coach was like, 'You know what, we’ve got to try something new.’ And he looked, turned at me and said, ‘Marcus, guard him,'" Smart recalled. "And that’s all he said. I just kind of looked like, ‘OK.'"

What else was the soft-spoken 22-year-old supposed to say? His teammates offered some reassurance and advice -- "stay down and force him into help," and "play with your hands back" -- and Smart went on a 14-minute stretch that propelled him into the national spotlight.

Smart limited Millsap to two points on 1-of-5 shooting the rest of the night, capping a performance in which, as the primary defender, he limited the Hawks to 1-of-10 shooting overall and forced two turnovers. Smart also scored 11 of his 20 points in the fourth quarter, helping Boston force overtime; the Celtics emerged with a 104-95 triumph that evened this first-round series at two games apiece.

Smart was so quick to dress after Sunday's game that teammate Isaiah Thomas wasn't ready when the interview podium opened for Boston players. Smart, in a black-and-white hooded sweatshirt unbefitting a player who expected to land in front of cameras, stepped up on the riser alone and shrugged away his individual impact in helping Boston to a win that may have saved its season.

On the front of Smart's sweatshirt, it read, "The revolution will not be televised." Which was a lie, because the world got an up-close glimpse at Smart's tantalizing talent. He was a tornado of late-game activity, making a hard charge at the basket for an and-1 layup and then storming the baseline for a springy, two-handed jam. And at the other end, he spent his time leaning on Millsap, doing whatever he could to deter Atlanta's power forward from scoring more points.

As teammate Evan Turner said, "[Smart] kept [Millsap] on 45 for, like, 20 minutes. That sounds crazy, but Smart stopped him from getting 50. Make sure you put that in the paper."

Down one sleeve of Smart's postgame sweatshirt, it read, "Breathe in, breathe out." And Smart could have easily lost his composure when he stumbled a bit on one Millsap backdown with about 5 minutes, 35 seconds to go. But that would be the only points he allowed on the night. And, to atone, Smart sandwiched a pair of 3-pointers around the Millsap make.

On Smart's other sleeve, it read, "Rise against the haters."

For all of his obvious potential, Smart has plenty of detractors, particularly those who wish to judge him based simply on his shooting percentages, ill-advised propensity to flop and occasional boneheaded lapses in judgment.

Yes, Smart shot just 28.9 percent (77-of-266) at TD Garden this season, finishing a season with the lowest field goal percentage at home in nearly six decades (St. Louis Hawks' Jack McMahon finished at 28.2 percent during the 1957-58 season, according to Elias Sports Bureau research). Yes, Smart earned a $5,000 fine from the league for turning himself sideways in a hilariously bad attempt to foul out Kyle Korver in the final minutes of Game 3. Yes, his foul late in Game 1, when Boston had a chance to play for a stop, hurt the team's chance to steal a victory.

And yet on Sunday, Smart showed why he's maybe Boston's best hope for a homegrown superstar. There's something special about him that can't quite be captured without seeing the whole picture. He has an insatiable desire to win, a thirst to compete. And in the biggest moment of the season, Stevens wasn't afraid to task the second-year guard with defending the hottest player on the floor.

When Thomas, with his two young sons in tow, finally reached the podium after Smart had already departed, he noted, "You give Marcus Smart an assignment, he’s probably going to get it done no matter who he is playing against. He’s a hell of a competitor."

Added Thomas: "[It's] like he’s been here before. Sometimes we have to tell him to calm down, but, more times than not, he’s comfortable in those situations, whether he has the ball, whether he doesn’t, whether he has to guard the best player on the other team. He’s going to be special in this league. And he’s only 22 years old, so imagine in a few years what he’s going to be like."

Stevens showered Smart with praise, but admitted that Millsap was probably pretty tired after scoring as much as he did over the first three quarters. Smart couldn't deny that. But Millsap gave the youngster credit when he claimed, "He is a tough guy."

Smart makes some basketball observers uncomfortable because he defies the traditional. Smart, the No. 6 pick in the 2014 draft who sports a rust-colored mohawk, doesn't have an obvious position because he doesn't shoot well enough to play off the ball and is still learning how to be an NBA point guard. Some wonder about his ceiling given his warts, but Celtics brass have been emphatic, saying he's a core piece of their future, maybe the most valuable player behind All-Star Thomas.

Smart's sweatshirt at the postgame podium was a fine reminder that he's anything but the norm. But that's exactly what makes him so darn interesting.

"I’m a basketball player," he said. "I don’t really define myself as any position, and I think that’s what’s been so unique about me growing up and playing ball. It’s kind of hard to define my position, and it’s kind of hard to see who you’re going to put on me. ... As crazy as it sounds, yes, I’ve guarded a 7-footer [in Knicks rookie Kristaps] Porzingis and things like that. And going to guard other bigs, and then covering the guards, it’s tough. But I pride myself on defense and this team knows that, my teammates know that, and the coaches know that. And they trust me to do that."

Smart knows he's not the norm. And he knows that probably causes his own coach some anxiety at times.

"I think I’ve given every coach I’ve played for a heart attack at least once," he said. "But what player hasn’t? You’re going to mess up. You’re not perfect. But there’s definitely a line between being aggressive and in control. You’ve got to determine between the two. You can be aggressive while still in control. And I did get out of control a little bit tonight, but for the most part, I stayed pretty much in control."

And his coach is perfectly fine with that if he can defend like he did on Sunday night.

"His aggression, his competitiveness, his spirit, like, our team needs it," Stevens said. "So, yeah, there’s going to be some times where he might take a shot or whatever the case may be that he’d like to have back, but he does a lot of good things that lead to winning and give you a chance to win. And defensive versatility’s at the top of that list."