Rondo scored a career-high 32 points to go with 10 assists on his 23rd birthday in Boston's 128-108 victory over the Suns on Sunday.
"As Rondo goes, this team goes," Celtics All-Star Paul Pierce said. "If he plays as well as he's playing, then there's no way we can lose."
Each team was without an All-Star starter because of injury. The Celtics did just fine without Garnett. Phoenix sorely missed Amare Stoudemire.
"We've got a lot of work to do," Suns point guard Steve Nash said.
Ray Allen scored 31 and Pierce 26 in Boston's first game since Garnett went down with a strained muscle in his right knee that is expected to sideline him for at least two weeks.
"Guys step up and play their roles even better when Kevin is out," Rondo said.
Phoenix will have a much tougher time compensating for the loss of leading scorer and rebounder Stoudemire following eye surgery on Friday. He won't be able to resume physical activity for about eight weeks.
The Celtics blistered Phoenix with 63 percent shooting. Rondo made 13-of-18 and Allen 10-of-15. After going 1-for-8 in the first half, Pierce was 7-for-9 in the second. He was 10-for-10 at the foul line.
The catalyst was Rondo. The Suns had no one who could defend him.
"Going into the game we thought that Rondo's speed was a huge advantage for us," Boston coach Doc Rivers said. "I told him to be just ultra-aggressive, just attack, attack, attack."
Jason Richardson scored 21 for the Suns in their first loss in four games under new coach Alvin Gentry. Nash added 19 points and 11 assists. Leandro Barbosa scored 18 and Shaquille O'Neal 17 for Phoenix.
It was an end to a tumultuous week for the Suns that began with the firing of coach Terry Porter. His replacement Gentry returned the team to its old ultra-fast style, and the Suns went on to win three straight under the new coach.
"First of all, that is a really good basketball team with or without Kevin Garnett," Gentry said. "You can see they don't have a whole lot of weaknesses."
The Celtics improved to 10-0 when Rondo scored at least 18 points, and he had that before halftime.
Rondo scored 22 to help Boston build a 68-54 lead at the break. The Celtics led by as many as 21 in the third quarter. Phoenix cut it to nine twice, then faded at the finish.
Boston is 3-1 on a western road trip that still has stops at Denver and against the Clippers.
The Celtics went up 80-59 on Brian Scalabrine's layup with 8:42 left in the third quarter
Phoenix, though, scored the next eight and O'Neal's dunk cut it to 80-67 with 6:50 to play in the quarter. The Suns sliced it to 12 four times before Matt Barnes' 3-pointer made it 92-83 with 1:50 left. Rondo and Allen scored the final four points of the period, though, and Boston led 96-83 entering the fourth.
The Suns cut it to single digits once more when Richardson's 3-pointer made it 96-87 with 11:02 to play. Allen followed with a 3-pointer to ignite a 15-3 spurt that made it 111-90 on Eddie House's 3-pointer with 7 1/2 to play.
Allen made his firs five free throws to run his streak to 72, breaking Larry Bird's franchise record of 71. Allen missed his next attempt. ... There were 26 free throws in the first quarter, 43 in the first half. ... Gentry, Nash and O'Neal each drew technical fouls in the first half. ... Rondo's previous career best was 26 against the New York Knicks last Dec. 21. ... The Celtics haven't had a home game in two weeks, and won't play one until next Friday (against Indiana). ... Phoenix has not won more than three in a row all season. ... Boston improved to 7-4 on the road against the West.