For two seasons, Marcus Smart had shown signs of being a force on the court. But after two years filled with gaps of inconsistency, injuries, foul-plagued stints and massive shooting slumps, Smart wants to be an impact player with the Celtics this season.

WALTHAM, Mass. — The night was a glimpse into everything everyone had been told that Marcus Smart could be as an NBA player.

With nine minutes left in Game Four of a first-round series against the Atlanta Hawks, Celtics coach Brad Stevens turned to the 6-foot-4 guard as a last resort to slow down the 6-foot-9 Paul Milsap, who had already torched the Celtics for 40 points on the night. The second-year player was not only up to the task defensively — frustrating Milsap into 1-for-5 shooting the rest of the way — but also offensively when he scored 11 of his 20 points in the fourth quarter of a 104-95 overtime victory.

For two seasons, the Oklahoma State product had shown signs of being that type of force on the court. But those two years were also filled with gaps of inconsistency, injuries, foul-plagued stints and massive shooting slumps.

Now Smart is looking to show he is that player from that memorable playoff night at TD Garden night in and night out throughout a full season.

“This year is a big year,” Smart said following Tuesday’s first official practice of training camp. “It’s my third year. There is no more trying to get used to it. I know what to expect. It’s just time to bring it.”

Stevens has lauded the way Smart has brought it with his volume and intensity in practices ever since the team took him with the No. 6 pick in the 2014 draft. But getting that competitiveness to translate to effectiveness in games has been a litany of stops and starts. Smart hit some critical shots as Boston rallied into the playoffs during his rookie year, but was benched in the first-round playoff series against the Cleveland Cavaliers.

Last season, his middling shooting numbers regressed as he dipped from 36.7 percent overall as a rookie to 34.8 percent, while his 3-point shooting fell from 33.5 percent to 25.3 percent. This is from a player who attempted 45.9 percent of his shots from behind the arc.

Smart said at the beginning of the summer his main objective was to improve his shooting, claiming on Tuesday he has quickened his release and eliminated “a dip” in his shot with the help of Celtics director of player personnel Kenny Graves and video assistant Alex Barlow.

“I’m making sure I give myself a chance for the shot to go in,” he said. “There is a small room for error. So I’ve been just getting up reps.”

Smart’s transition from a boom-or-bust role player to a reliable cog in the lineup could be one of the biggest variables for the Celtics as they attempt to make the leap toward the NBA elite this season. With Evan Turner’s departure in free agency, there’s minutes to be had at both backup point guard behind Isaiah Thomas and backup small forward behind Jae Crowder, with Smart possessing the most versatile skill set of those vying for that time.

“Nobody is going to do exactly what Evan did,” Stevens said. “They may do some things. They may be more of a spot-up shooter. They may be more of a penetrator. It may be that we decide to go small. We may decide to go big. We’re going to play to the strengths of the individual and not necessarily try to fill a spot and be Evan.”

Celtics president of basketball operations Danny Ainge on Monday mentioned Smart, second-year point guard Terry Rozier and rookie Jaylen Brown as candidates to grab Turner’s vacated minutes, while Stevens tossed in recently reacquired forward Gerald Green to that mix while speaking at a University of Rhode Island coach’s clinic two weeks ago.

The coach added on Tuesday that the preference is for one or two players to separate themselves from the rest and earn those minutes out of training camp. Smart said he believes his breakout playoff performance, and his offseason work, will put himself in position to gain that space for a squad looking to climb from the middle of the Eastern Conference playoff pack.

“This year is real huge,” he said. “Not only for me, but for this team. This year is just big because we have the pieces. We know what it takes. We’ve been to the playoffs. We won games. We've beaten the best of the best on their home floors.

“Now we’ve got to be more consistent as a team and I’ve got to be more consistent as an individual.”