BOSTON -- Quiet, at least by last season's All-Star standard, through the Boston Celtics' first five games of the preseason, Isaiah Thomas put together a near-perfect first half on Monday night against the Brooklyn Nets and promptly declared himself ready for real basketball to start.

Thomas, who made all six shots he took while putting up 19 first-half points, passed time in the second half by excitedly cheering big moments for Boston's youngest players, sitting in the front row with fans trying to get on the JumboTron, and grooving when "Gino Time" rolled toward the end of a breezy 120-99 triumph at TD Garden.

After displaying the sort of basket-attacking aggression that distinguished his play last season and after another excellent showing for Boston's starting group, Thomas was asked to assess the prospects for the 2016-17 Celtics.

"We have a pretty good team -- a team that can make some legitimate noise," Thomas said. "And if we put it together and play the right way, we can make a lot happen this season. We don’t ever want to put a ceiling on it, but we have a really good team. I know that."

Isaiah Thomas and the Celtics had things rolling Monday against the Nets. Maddie Meyer/Getty Images

There's a lot to be optimistic about in Boston -- and that's before you even factor in the potential struggles of a Nets squad whose draft position the Celtics have the right to swap with in June. The two teams meet again here on opening night on Oct. 26.

Al Horford, Boston's summer splurge, is a team-best plus-64 in plus/minus through 84 minutes of floor time. The Celtics' starters funnel the ball through Horford on the offensive end and he has consistently generated quality looks for his teammates with his passing skills. On the other end, Horford strengthens a Boston defense that finished tied for fourth in defensive rating last season while serving as the back line anchor.

"He's an efficient player and he makes the open shot. He's a really good passer, a really good passer out of the pick-and-roll," said Nets coach Kenny Atkinson, who was an assistant in Atlanta the past four seasons and joked about getting emotional just talking about his time with Horford.

"And then he's going to make them better defensively, which is a little scary because of his pick-and-roll defense, and how he protects the rim. So he just -- all-around, he's going to help them get better."

While Celtics coach Brad Stevens has stressed his team has a long way to go to get where it desires to be, the potential for this team has been on display throughout the preseason. With a toy chest of versatile guards, Stevens has experimented with multiple small-ball lineups and found success with many of them.

Like in the first quarter Monday, Stevens made Marcus Smart the first sub, replacing Amir Johnson. Boston zipped the ball around with three guards -- Smart, Thomas, and Avery Bradley -- as Jae Crowder shuffled to the forward spot alongside Horford. In the second quarter, Stevens came back with a three-guard lineup that had Thomas playing alongside newcomer Gerald Green (that tandem that had success two seasons ago in Phoenix) and Terry Rozier, a second-year guard who has made the most pronounced leap on the team and is ready for rotation minutes.

Rozier adds a combination of athleticism, ball-handling, shooting and, most notably, quickness to the floor. As Stevens offered after Monday's game, "I'm a big fan of speed."

Will the bite-sized chunks of positive play translate to the regular season? Thomas and his teammates seem to believe so. Many of Boston's biggest concerns coming into the preseason -- such as the departure of sixth man Evan Turner -- have been eased by the play of Rozier, Smart and No. 3 pick Jaylen Brown (a player Boston selected with the Nets' 2016 draft pick).

Much of the focus in Boston has turned to the nip-and-tuck battle for the final roster spot. The team has 16 guaranteed contracts and must trim to 15 by the start of the regular season next week. Complicating matters, Boston's youngest players -- including second-year guard R.J. Hunter and third-year swingman James Young -- have each had solid moments. Hunter put up a team-high 17 points on Saturday in New York; Young came back with 10 points in Monday's win.

Stevens would contend there's much bigger issues to deal with, but when the biggest question mark on the team is the 15th man, that's an encouraging sign for the Celtics.

Boston still needs to get backup big man Kelly Olynyk healthy (he's rehabbing from shoulder surgery this summer), concerns remain about whether the team can consistently rebound while playing undersized lineups, and the Celtics have been prone to lulls in intensity after building leads in these preseason games.

After Wednesday's exhibition finale against the Knicks, Stevens will get a week of practice to fine-tune everything.

Said Crowder: "We'll be ready come the first game."