BOSTON – Marcus Smart is no stranger to generating an increase in the heart palpitations of whoever is coaching him.

But there are nights like Game 4 against the Atlanta Hawks when he simply takes your breath away with his play at both ends of the floor.

A strong night from the second-year guard was just what the Boston Celtics needed to beat the Hawks 104-95 in overtime.

"A defensive spark. He's unbelievable," teammate Evan Turner told reporters after the win. "When he starts scoring offensively and he gets his playmaking down, he'd be an exciting player to watch. I thought tonight he was the best player on the court."

Now the best-of-seven series shifts back to Atlanta to where it’s now tied at two games apiece with Game 5 set for Tuesday night at 8:30 p.m.

The contributions to this victory were numerous for the Celtics, but none stood out more than those made by Smart who came off the bench and scored a playoff career-high 20 points on 7-for-15 shooting.

And just as significant was his defense in the fourth quarter on Paul Millsap, who led all scorers with 45 points but was scoreless for the final 1:44 of the fourth and all of the overtime session.

Smart, who acknowledged he was surprised when he got the assignment to try and limit Millsap down the stretch, said his goal in defending the three-time All-Star was pretty simple.

“To really stop and make it hard for him, pressure him and really contest every shot that he took,” Smart said.

As important as Smart’s defense on Millsap was to the game’s outcome, his fourth quarter scoring was arguably just as valuable.

Millsap drained a 23-foot jumper that gave Atlanta an 80-74 lead with 9:35 to play in the fourth quarter.

From there, Boston went on a 13-4 run with Smart scoring the first 11 points during the spurt.

“I’ve got to give credit to my teammates for that,” Smart said. “Isaiah (Thomas) did a heck of a job, the way that they were guarding him, still being able to penetrate and find guys and I was one of those guys on the end of that. When I was that wide open and Isaiah doing all that work, I had to make the shot. Definitely it was one of the best rhythms I’ve had all year.”

His teammates echoed similar sentiments about his impressive performance.

“He stepped up big-time for us tonight,” Celtics center Amir Johnson told CSNNE.com. “He really had it going for us in the fourth quarter (in Game 4).”

Smart’s breakout performance came just 24 hours after the NBA fined him $5,000 for a flop in Game 3, the kind of play that serves as a reminder of how the 22-year-old will at times make plays that leaves you just scratching your head wondering, ‘what was he thinking?’

But the body of work that Smart puts together from one game to the next, has a way of making those who depend on him the most – his teammates and his coaches – look beyond those incidents and instead focus on what he brings to the game in its totality.

“His aggression, his competitiveness, his spirit, our team needs it,” said Celtics head coach Brad Stevens. “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.”

Smart will be the first to tell you that he tends to walk that fine line between being an aggressive, impactful difference-maker at both ends of the floor, and a player that gives his coaches a heart attack with some of the inexplicable decisions he sometimes makes on the floor.

“I think I gave at least every coach I’ve played for a heart attack at least once,” quipped Smart. “But what player hasn’t? You’re going to mess up, you’re not perfect but it’s definitely a line between being aggressive and being in control. You got to determine between the two; you can be aggressive while still in control and I did get out of control a little bit (in Game 4), but for the most part I stayed pretty much in control.”

And by doing so, he played a significant role in positioning the Celtics to take control of this first-round series with Game 5 in Atlanta on Tuesday night, a series whose momentum seems to have swung in Boston’s favor.