BOSTON -- The Toronto Raptors, favorites to repeat as the winner of the Atlantic Division, are off to a 2-0 start.

But that doesn't mean coach Dwane Casey is completely happy.

"We have to do something about the slow starts," Casey said after his team topped the Boston Celtics 113-103 on Friday night.

Slow starts? The Raptors trailed the Indiana Pacers 30-20 at the end of the first quarter in Wednesday's opener in Toronto. Then, Friday night, they fell behind 10-4 in the opening minutes and really couldn't do anything right for five minutes.

They fought back to tie at the end of the quarter and were tied at the half despite shooting 32.5 percent from the floor.

Then, thanks to the hot hands of forward DeMarre Carroll and swingman Terrence Ross, they took off.

Ask them what happened and they point to their defense.

"Defense leads to offense," said Carroll, who signed with the Raptors as a free agent over the offseason. "Our main focus is defense, defense, defense."

Carroll scored 21 points, 10 of them in a 4:12 span of the third quarter, and Ross poured in 13 in the fourth quarter to lead the offense.

Carroll, who had 14 points, eight rebounds and four assists in Toronto's opening victory, was 4 of 7 from 3-point range and his third-quarter outburst helped his team turn a halftime tie into a 9-point lead.

"I thought the third quarter was when it kinda got away," said Boston coach Brad Stevens.

From there, Ross took over, scoring 13 of his 21 points in the first 7:22 of the fourth quarter. His 3-point bomb gave the Raptors a 101—84 lead with 5:51 remaining.

Ross, who came off the bench, was 8 of 12 from the floor.

"Coming off the bench helps me see what the team needs help on," Ross said. "I actually like it better. Come into the game, make a quick impact and go from there."

The Raptors built their lead to 19 with 4:05 left. The Celtics closed the deficit to nine but a Carroll put-back with 1:33 left sealed the victory.

Swingman DeMar DeRozen scored 23 points, grabbed seven rebounds and dished out six assists for the Raptors, while guard Dwight Lowry added 14 points, nine assists and seven rebounds forward Luis Scola had nine points and nine rebounds and center Jonas Valaciunas grabbed 10 boards.

The win was the 156th with the Raptors for coach Dwane Casey, tying him with Sam Mitchell for the club record.

Guard Isaiah Thomas came off the bench to lead the Celtics (1-1) with 25 points and seven assists, but was just 7 of 16 from the floor after also struggling with his outside shot in a 25-point opening performance. Guard Avery Bradley led four others in double figures with 13 points, grabbing five rebounds.

"They just came out and played harder than us," Thomas said of the third quarter. "They wanted it more in the start of the second half. That's what it was offensively and defensively."

The Celtics missed nine free throws and were just 7 of 26 from 3-point range in the game. Toronto went 11 of 26 from behind the arc.

Forward Amir Johnson, who left the Raptors for Boston as a free agent, had 11 points and eight rebounds in his first game against his old team.

There were three technical fouls in a 32-foul first half, two on Celtics players.

The teams went on to combine for 61 fouls in the game.

NOTES:: The Celtics picked up the third-year contract options on G Marcus Smart and G James Young and the fourth-year option on F Kelly Olynyk. ... Olynyk, who missed Wednesday's opener while serving a one-game suspension for his playoff grab-and-yank on Cleveland Cavaliers forward Kevin Love's arm, made his season debut Friday. ... With the win, Toronto coach Dwane Casey matched Sam Mitchell for the most wins in Raptors history with 156. "In the NBA you're only as good as your last game," Casey said. "In our business, it's sad, but nobody appreciates the building, what we started, where we are now. All they remember now is that last game." ... Celtics rookie R.J. Hunter, who missed his NBA debut because of illness, was ready after what he thinks was food poisoning. "You hear all the jokes like 'you were too nervous to play.'" he said before the game, which was attended by his dad, Georgia State coach Ron Hunter, who flew in after his team's practice. ... On Sunday the Raptors host the Milwaukee Bucks, while the Celtics complete their season-opening three-game homestand against the San Antonio Spurs.