DENVER -- Brad Stevens was not happy with his team's defense over the past few games.
The Boston coach had nothing to complain about after the way the Celtics played Sunday.
Boston played lockdown defense for most of the night, forcing 24 turnovers and cruising to a 121-101 win over the Denver Nuggets.
"We were really good the whole night," Stevens said. "For the most part we played 38 minutes about as locked in as we've played in a while. You could tell there was a purpose, a good pride about us the whole day."
That defensive effort was necessary after the Celtics allowed an average of 119 points in going 2-2 in their previous four games.
"We understood what we had done the past couple of games and we stepped it up on defense," Sullinger said.
Guard Avery Bradley added 20 points for the Celtics (33-24), who have won 11 of their last 14 games to stay on the heels of first-place Toronto in the Atlantic Division. Boston had a 48-36 edge in rebounding despite being undersized against Denver.
The Celtics also had a 97-73 advantage in field-goal attempts.
"We sucked," Denver guard Emmanuel Mudiay said. "They had more energy than us from the jump. They scored a lot of points off our turnovers and on fast-break points. That's what they do. That's what they're good at."
Center Nikola Jokic had 23 points and 13 rebounds and forward Danilo Gallinari scored 17 for Denver, which has lost its first two games out of the All-Star break.
"I'm feeling good and I am still trying to learn the plays and get used to my teammates," Augustin said. "It's going to take some time."
It was another poor defensive performance for the Nuggets. They allowed 70 first-half points to Sacramento on Friday and 64 to Boston and never led after the first few minutes of the game.
Sunday, in a rare matinee game, the Nuggets (22-34) fell behind 51-25 in the second quarter. They dug out of the 26-point deficit with a 13-3 run to start the second half, and Jokic's 3-pointer made it 67-62.
They had a chance to cut it to three on a fast break, but Thomas blocked Gallinari's shot from behind to spark a 9-2 Boston run that pushed the lead to 12.
Thomas, who had 10 of his assists in the first half, finished with two steals and three rebounds.
"He was good," Stevens said. "He made the right play most of the time, especially in the first half when he had 10 assists."
The Nuggets tried to fight back early in the fourth quarter but the Celtics kept making plays. Leading by 13, guard Marcus Smart stole the ball from Denver center Jusuf Nurkic in the lane and guard Evan Turner ran to the other end of the court to save it to Bradley, who hit the layup to make it 97-82 with 10 minutes left.
"It was an amazing play," Sullinger said. "It was winning basketball."
Denver got within 10 with 7:05 left, but Thomas hit a 3-pointer and made all three free throws when he was fouled on a 3-point attempt to push the lead to 109-94.
"Our defense is still somewhere in the Caribbean," Denver coach Michael Malone said.
NOTES: Celtics F Kelly Olynyk missed his second straight game with a right shoulder sprain. ... Nuggets G D.J. Augustin took part in his first practice since coming to Denver from Oklahoma City in a trade Thursday. Augustin didn't join the team until after Friday's morning shootaround in Sacramento. He was able to take part in Saturday's light practice and Sunday's shootaround. ... Boston is 7-7 in the first game of back-to-backs and 10-3 on the second night. The Celtics are at Minnesota on Monday. ... Nuggets F Darrell Arthur played his second game after missing five with an injured left quad. Coach Michael Malone said he showed rust Friday but added, "Those shots will start to fall."