By Matthew Geagan, CBS Boston

BOSTON (CBS) — It’s safe to say the Celtics starting five is going to be pretty darn good this season, whoever it may be that lines up alongside Kyrie Irving, Gordon Hayward and Al Horford.

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The new-look Celtics will certainly need some time to mesh with each other, but the squad should be able to lead Boston to a deep playoff run. The biggest question, aside from the chemistry of those new players in the starting unit, is what the Boston bench will be able to provide when the studs aren’t on the floor. That will be a fluctuating topic throughout the year, with Brad Stevens mixing and matching to find the best possible group for those stretches. Even the mastermind coach won’t truly know what he has until the regular season tips off with all of the fresh faces in town, a handful of which have never played in a real NBA game before.

But with two of the longest-tenured Celtics expected to lead the way off the pine, Boston should be in pretty good shape with their reserves. We got a great glimpse of the bench’s capabilities in Monday night’s preseason tilt against the Philadelphia 76ers, as the Irving-Hayward-Horford trio enjoyed an evening off and let the bench squad get most of the run. Led by Marcus Smart and Terry Rozier, the Celtics came out with heaps of energy and never looked back in what quickly became a laugher of a preseason affair.

Rozier dazzled in his 23 minutes on the floor, racing to 15 points, 10 rebounds and six assists. Smart was his usual pesky self on the defensive end with a pair of steals (including one of his patented aggressive swipes where he ripped the ball away from a driving Markelle Fultz) and a block, while also showing off his much-improved jump shot. The fourth-year guard hit five of his eight attempts from the floor, including two of three from downtown, to finish with 12 points and six rebounds on the night.

It’s pretty scary to see that two players with five combined seasons have been wearing a C’s uniform longer than anyone else on the roster, but that’s where the team sits after Danny Ainge’s transaction binge over the summer. The duo of Smart and Rozier are being handed the keys to the Boston second unit, and while it’s unclear who will be rounding out the rest of that squad (other than No. 3 overall pick Jayson Tatum), the two guards are going to provide Boston with a truckload of energy whenever they’re sent on the floor.

“I just think they bring a lot when they’re on the court together and, again, the energy that they play with, the way that they can lift you on offense and defense,” Stevens said after Monday’s win. “Terry’s defense has made really good strides and it’s a credit to him. And I think part of it is you’re in the league another year and you just become more experienced and more used to it. So hopefully that can be a real uplifting group for us; they certainly led the way tonight.”

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“We play with each other a lot and we’ve had a lot of practice going up and down so I think our chemistry is getting there, we still have a long way to go,” said Rozier, who finished a plus-25 in the win. “We are going to fly around and play hard and everything else will take care of itself. We got a lot of guys that can play hard out there.”

A big part of both of their games (especially Smart’s) is confidence and poise. They showed plenty of both as Rozier glided through the air for easy layups and Smart’s rambunctious game displayed plenty of polish. His jumper looks like an actual jumper, and he also seems more willing to drive to the hoop. Smart went hard to the basket early in the game, going right at Philly big man Jahlil Okafor before putting it in off of the glass, something we’d like to see more of out of the guard.

Smart has plenty of incentive to have a big season for Boston, as he’s likely looking at restricted free agency this summer. There’s a chance that he could see some time in the starting lineup at shooting guard, giving the Celtics a strong defender to play alongside Irving, but he’s better fit as the leader of the C’s reserves. He said the biggest part of the second unit’s success this season will be keeping their emotions in check and waiting for their opportunity to come.

“We are a young and athletic with fresh legs, so everyone is anxious to go out and show what they can do,” he said. “We have to be patient and let the game come to us. I think we did a good job at that tonight, being the third preseason game.”

That pressure will obviously ramp up when the regular season tips off next week, and there will be plenty of bumps along the way as Stevens tries to figure out which lineups work best and when. He’s got his work cut out for him as he tries to piece together not only a new starting lineup but a bench he can count on. He has a collection of reserves in Guerschon Yabusle, Daniel Theis, Semi Ojeleye and Abdel Nader who could help provide that bench spark, but have yet to play any meaningful minutes in the National Basketball Association. That’s where Smart and Rozier, and all five years of their NBA experience, will be needed most.

Stevens has a lot of work with just a week ago until the regular season gets underway, and Boston’s rotation and lineups will be a work in progress for a while. But he should feel pretty confident penciling both Smart and Rozier into that second unit, a duo that will have no problem providing an energetic boost off the bench.

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