Stoudemire scored 13 of his season-high 29 points in the decisive third quarter, and the Suns matched the best start to a season in franchise history with a 113-94 victory on Friday night.
Marion added 21 points, 17 rebounds, five steals and two blocked shots.
"Amare got it going on the offensive end, and I got it going on the defensive end," Marion said.
The Suns' 11-2 start matches the franchise record set in 1980-81 and equaled in 2004-05. They can break the record with a victory at Golden State on Monday.
"I don't think we're playing as great as we have in certain streaks in the past," Steve Nash said, "but we're still building. It's early in the season, so the record's great considering."
Nash added 20 points and 10 assists, and Grant Hill scored 19 points for the Suns.
Cassell had 26 points through three quarters, then sat down for good.
"He played great," Clippers coach Mike Dunleavy said, "but when they jumped out on us, we play tomorrow night in back-to-back games, I just felt like I didn't want to take any more of his legs."
Dunleavy said if his team cut the lead to single digits, he would have put Cassell back in. Actually, the Clippers cut it to eight with 2 1/2 minutes to go, and still Cassell sat. And the 38-year-old guard didn't like it.
"I don't dictate plans around here," Cassell told reporters. "The only thing I dictate I do on the court. I was sitting there like you guys, I can't do nothing. But it is what it is. We move on to the next game."
Phoenix's ultra up-tempo offense wasn't nearly as jaw-dropping as it was against Sacramento on Tuesday night, when the Suns scored 47 in the first quarter and 80 in the first half. But things picked up for Phoenix in the second half.
"We came out and swarmed them," Suns coach Mike D'Antoni said. "Shawn was all over the place. He literally doubled and rebounded and got loose balls and did an unbelievable job of picking our energy up."
Down 52-51 at the half, the Suns took the lead for good with a 9-0 run early in the third quarter. Stoudemire scored eight in the surge, starting it with a three-point play and ending it with an inside basket that gave Phoenix a 63-54 lead with 9:15 left in the quarter.
"The second-half intensity was definitely very important to us," Stoudemire said. "The first five minutes is what we keyed on, and we were able to get it going."
Another three-point play by Stoudemire put Phoenix ahead 84-69 with 1:24 to go in the third, and the Suns led 86-74 entering the fourth.
Raja Bell started the final period with a 20-footer, Marion stole the ball from Dan Dickau and dunked, then Stoudemire scored inside and Phoenix led 92-74. The Clippers cut it to 102-94 when Kaman scored inside with 2 1/2 minutes left.
Bell responded with a 3-pointer, and the Suns scored the last 11 points of the game.
Dunleavy said he probably made a mistake by playing Kaman too many minutes in the first half. The big center acknowledged he was worn out down the stretch.
"At the end of the game, I was pretty tired," Kaman said. "I wasn't finishing some shots I normally finish, which is pretty disappointing for me. I didn't make my free throws. I was too tired."
Cassell scored 18 in the first half on 6-of-10 shooting, including 2-of-2 3-pointers.
The Clippers, playing without injured Elton Brand, Corey Maggette and Shaun Livingston, led 25-16 with 3 1/2 minutes left in the first quarter. The Suns caught up in the second, and led 49-46, but Los Angeles outscored Phoenix 6-2 the rest of the quarter to lead 52-51 at the break.
The Clippers are 2-5 since a 4-0 start. ... Bell was back in the Phoenix starting lineup after missing two games with an aching back. He sat out two of three games before that with a sprained right ankle. ... The Suns' Leandro Barbosa scored just six points on 2-for-10 shooting. He was 0-for-5 from 3-point range.