BOSTON -- Life after Tim Duncan continues to go quite well for the San Antonio Spurs.

Duncan, one of the NBA's greatest players, will have his No. 21 retired next month. Meanwhile, the coach and players he left behind and some new faces are doing just fine -- and just kept on rolling with a spirited win 109-103 over the Boston Celtics on Friday.

"It was a great win for us against the really active team," Spurs coach Gregg Popovich said after the Spurs (13-3) extended three winning streaks with the hard-fought victory.

The Spurs, who trailed by 14 points in the first half, rallied for their eighth straight win overall, their ninth in as many road games this season -- and also beat Boston for the 10th consecutive time.

Oh, and they ended Boston's three-game winning streak.

Kawhi Leonard, who finished with 25 points, 10 rebounds and four assists, scored nine points in the fourth quarter -- all in the final 7:17 -- as the Spurs improved to 13-3.

The San Antonio bench totaled 56 points and 17 rebounds, with Patty Mills scoring a season-best 19 points and rookie Davis Bertans and veteran David Lee adding 15 points apiece -- a career high for Bertans and season high for Lee, who turned back the clock and also grabbed a season-high 12 rebounds in just 17:31 of playing time.

Lee may have been seeking revenge against the Celtics, who had him at the start of last season and hardly used him before he finished the season in Dallas.

"He's been playing really well," Celtics coach Brad Stevens said of Lee. "You kind of saw that toward the end of last year when he was with Dallas and he's been a really good fit."

Lee is in shape and with the Spurs, where Popovich tends to get the most out of players -- and where he plays the hot hand. He had Mills running the show down the stretch with Tony Parker on the bench.

"It did not work out the way I wanted it to, these things sometimes happen," Lee said of his stay in Boston. "Obviously, I really respect the people and the organization, the guys on the team. I made sure to say hello to every single guy on the team as well as the coaching staff. Said hello to Brad, so there are no hard feelings on my end. I believe it is the same way on their end.

Starters Danny Green and LaMarcus Aldridge scored 11 and 10 points, respectively, with Aldridge clinching the outcome with an offensive rebound and two free throws with 17.4 seconds remaining.

Isaiah Thomas led the Celtics (9-7) with 24 points and eight assists while Avery Bradley had 19 points and eight rebounds. Al Horford added 12 points, 10 rebounds and three blocks while Marcus Smart, coming off the bench, had nine points, 10 assists and four rebounds.

"We had to play a little bit better to win that game against a really good team," said Stevens, who was happy his team had 32 assists on 42 baskets and turned the ball over just 10 times -- while San Antonio coughed it up 17 times. But the Celtics shot just nine free throws, compared to 25 by the visitors (22-for-25).

"I felt like we fought really hard all night," said Horford. "I think the stat sheets say their bench was the difference. They did a great job."

The Celtics used an 18-2 first-quarter run to grab a 24-10 lead. Boston had a similar start in its last game at Brooklyn, where a 17-point lead was squandered in a game Boston won.

This time, the Celtics, coming off sweeping a three-game road trip, went 5:51 without a point in the second quarter as San Antonio used a 12-0 spurt to get back in the game. Boston then needed 2:37 to score in the second half, running that drought to 3:38 bridging the halves as the Spurs built an eight-point lead.

NOTES: Spurs coach Gregg Popovich on his team being 8-0 on the road and 4-3 at home before Friday's win: "It's a weird year. We lost three in a row at home, and last year we lost one all year. Now we're undefeated on the road. Don't ask me. I guess that's why they call it a game. You never know what's going to happen." ... Celtics coach Brad Stevens, asked why his team swept a three-game road trip, said: "Health. It's nice to have everybody back." ... Celtics C Al Horford, who recently returned from a nine-game absence (concussion), has scored 67 points, grabbed 32 rebounds, dished out 22 assists and blocked 11 shots in four games back. ... Boston F Jae Crowder, who recently missed eight games with a sprained ankle, scored 18 points in his fourth game back. ... The Spurs finish their three-game trip at Washington on Saturday night, while the Celtics are off until Monday night's game at Miami.