BOSTON — The Boston Celtics are once again looking like the team that won 19 in a row before an uncharacteristic midseason slump had people asking what was wrong with the defending NBA champions.

Rajon Rondo had 23 points and seven assists before sitting out the fourth quarter with the rest of the starters, and Boston opened a 30-point lead before coasting to a 104-87 victory over the Phoenix Suns on Monday night. The Celtics have won five straight since a 2-7 slump that was the worst stretch of the new Big Three era.

"I don't think this is a team that will get shaken or rattled when we go through a struggle," said Paul Pierce, who had 12 points, eight rebounds and eight assists. "We stay together and we kept our heads up. I never really thought we lost our confidence. We're still the defending champions. It's just a matter of remembering who we are as a team."

The Celtics won their 17th NBA title last season and began this year as if they would cruise to No. 18, winning 27 of their first 29 games for the best start in league history. But they lost a Christmas Day rematch with the Lakers, their opponent from the NBA finals, and then lost six more times in a two-week span.

Home-and-home victories over Toronto and New Jersey were nice, but Monday's win was the first over a team that's now above .500 since Dec. 17 against Atlanta.

"I just like where we're going right now as a team," Celtics coach Doc Rivers said.

Pierce scored all of his points by halftime to help Boston take a 64-34 lead. Ray Allen scored 20, and Kevin Garnett had 16 points with eight rebounds.

"It was a good ol' spanking. That's what is was," said Suns coach Terry Porter, who called it his team's worst loss of the year. "They came out and turned on the intensity on us early and we didn't respond. They got whatever they wanted. There was no resistance from us whatsoever."

Shaquille O'Neal scored 16 with 11 rebounds for Phoenix, which had won seven of its last 10. Amare Stoudemire, the Suns' leading scorer this season, had just three points on 0-for-7 shooting.

Little-used Brian Scalabrine, who started because Kendrick Perkins missed his fifth straight game with a sore shoulder, guarded Stoudemire. Garnett and Glen "Big Baby" Davis shared the workload on O'Neal.

"It was like holding up a wall," Garnett said. "Go home, knock out the foundation in your house and hold up the wall. When it's about to fall on you, that's what it's like guarding Shaq."

Pierce scored the first six points, and Rondo also had six points early to help the Celtics open a 21-lead 7 midway through the first quarter. They led 30-15 after one, then scored 17 of the first 21 points in the second to open a 47-19 lead.

"They put on a clinic for us tonight," said Steve Nash, who had 12 points and eight assists.

Pierce rolled his right ankle in the second quarter but remained in the game.