TORONTO -- When Dwane Casey arrived as head coach of the Toronto Raptors in 2011, he put a 1,300-pound boulder in front of the team's locker room and introduced the concept of "Pound the Rock."

Casey was hired after winning a championship with the Dallas Mavericks as an assistant coach, with a defensive reputation. The Raptors have made the playoffs in each of the past three seasons, including a trip to the Eastern Conference Finals last year, but the defensive progress has been up and down during the three-year stretch.

After a first-round loss to the Brooklyn Nets in 2014, James Johnson was brought in to strengthen the team's perimeter defense. The following year, Toronto gave up a league-worst 112.5 points per 100 possessions in a four-game sweep at the hands of the Washington Wizards in the first round, and shored up their defense further by signing DeMarre Carroll in the offseason.

Last year, Toronto finished the regular season 11th in defensive efficiency. This year, Toronto has slipped to 16th in defensive efficiency, one of the big reasons they lost 11 of 16 games before the All-Star break.

The second half of the season, with 25 games remaining on the schedule, presents a reset opportunity for this team, and general manager Masai Ujiri has bolstered the roster with two players with defensive reputations, trading for Serge Ibaka and P.J. Tucker in a week's span. This is arguably the deepest Raptors roster Casey has coached in Toronto, but the Raptors also face the challenge of chasing down both the Celtics and Wizards in the Eastern Conference. As it currently stands, Toronto is in fourth place, which means a potential second-round matchup against LeBron James and the Cleveland Cavaliers. For a team that has finally nudged themselves toward win-now mode, the unofficial goal is to position itself for another deep playoff run, and make a move for a top-two seed.

The second-half marathon, as Casey described it, began on Friday at home against the division leading Celtics, with both Ibaka and Tucker making their debut. Prior to the game, Casey was in no mood to talk about any adjustment periods for his new players.

"Step up, be leaders," Casey said when asked about the message he sent to his two new players. "You guys have been in this league."

Tucker, who found out he was traded on Thursday afternoon and arrived in Toronto without any sleep on Friday morning, admitted he was already comfortable. "You lead by example first and show them what you mean," Tucker said. "Then later, you tell guys what you mean, and what you need to do in certain situations."

Those words rang true as the Raptors erased a 17-point deficit against the Celtics in the second half on Friday night. In the fourth quarter, Tucker -- who played 29 minutes and scored nine points, grabbed 10 rebounds and added three steals -- was on the floor as the Raptors held the Celtics to 20 points, including a signature sequence where the new Raptors forward ripped the ball from Isaiah Thomas late in the game. Ibaka, who made his own defensive impact with 15 points and seven rebounds, was also part of the closing lineup that gave the Raptors a new feel on the defensive end, with individual defenders capable of locking down their opponents and with the flexibility to switch on matchups. The Raptors outscored the Celtics by 13 points in the fourth quarter and got a much needed 107-97 win at home.

The physicality and toughness that Casey has been talking about repeatedly during his tenure in Toronto was on full display against Boston. In the first half, DeMarre Carroll and Thomas got into a scuffle. In the closing stages of the game, Tucker and Ibaka led the way on the defensive end.

"It's more than just hitting people," Tucker said before the game. "Toughness is mental."

The Raptors will need to embrace this new identity even more after finding out their starting point guard Kyle Lowry will be out with a right wrist injury, which will be evaluated over the weekend. The injury was suffered a week ago Wednesday in a victory over Charlotte. Lowry received treatment during All-Star weekend, in which he participated in the three-point shootout and the All-Star game. The wrist was still sore after Lowry did some shooting on Thursday, though.

The Raptors are a different team without Lowry on the floor. Per NBA.com, the Raptors headed into Friday's game outscoring opponents by 8.1 points per 100 possessions when Lowry was in. Without him, they had a net rating of -5.3. It's reflective of how important their point guard is, as it showed during last year's playoffs, when Toronto was outscored by 27.6 points per 100 possessions when Lowry was on the bench.

The offensive end should not be a concern for Toronto, as DeMar DeRozan carried the load in Friday's win, scoring a career-high 43 points on 15-for-28 shooting, hitting huge baskets down the stretch to move the Raptors within three games of the Celtics.

"I have to be a little bit more aggressive," DeRozan said of Lowry's absence, "and just pick and choose my spots."

Without Lowry, it becomes even more imperative for the Raptors to shore up their recent defensive flaws.

The closing stretch of the fourth quarter against the Celtics provided a glimpse of what the Raptors' potential could be on that end of the floor. With the addition of Tucker and Ibaka, along with players like Norman Powell, DeMarre Carroll and Cory Joseph, this is the path toward a deep playoff run.

"One thing you can't learn is playing hard," Ibaka said. "And that's what we did."

Tucker can see where the Raptors can go once Lowry returns.

"We've got so many weapons and so many possibilities," Tucker said. "Defensively, I think we can wreak havoc. Throw Kyle in there, and we can really do some things and be special."

Now, with 24 games left on the schedule, the Raptors look to forge their identity and re-establish themselves as a legitimate contender in the East.