In a little under four minutes, backup quarterback Drew Stanton and the defense combined to score three touchdowns that rallied the Cardinals past the St. Louis Rams 31-14 Sunday and improved their record to an NFL-best 8-1.
Whether the Cardinals will need to try to keep winning minus Palmer was uncertain.
"We don't know anything about Carson's injury or the length, whatever it is yet," coach Bruce Arians said. "He will be evaluated and get an MRI and everything and we will know something by tomorrow and hopefully by Tuesday."
Palmer left with 11:28 to play and the Cardinals trailing 14-10.
"Defensively, we hung in there while our offense really struggled," Arians said. "Then we got turnovers we are all use to seeing, playing the type of fourth quarter we are use to seeing."
On the first possession after Palmer was hurt, rookie John Brown's diving grab of Stanton's 48-yard touchdown pass put the Cardinals up 17-14 with 7:40 to play.
"That is what I am here for," Brown said. "That is why coach Bruce Arians brought me in for, to make big plays. They say big-time players step up in big-time games so I try to do the best I can when it is my time."
Palmer was taken to the locker room on a cart after being helped off the field.
It was the same left knee that he injured Jan. 8, 2006, in a playoff game against Pittsburgh, when he tore his ACL and MCL on his first pass of the game.
"I think there's a question mark there because nobody knows what his status is," Stanton said. "It's difficult because he is the leader of this team. ... We'll just continue to weather the storm, whatever it is."
Patrick Peterson got his first two interceptions of the season, returning the second one 30 yards for a touchdown to make it 24-14. Moments later, Austin Davis fumbled and Antonio Cromartie returned it 14 yards for a score as Arizona outscored the Rams 21-0 in the fourth quarter.
St. Louis (3-6) was shut out in the second half.
At 8-1, the Cardinals have their best record after nine games since going 11-1 as the Chicago Cardinals in 1948.
Palmer was playing some of the best football of his career and, on Friday, signed a three-year contract extension worth a reported $50 million with $20.5 million guaranteed.
On third down at the Rams 28, Palmer dropped back to pass, then tried to avoid blitzing safety Mark Barron. The quarterback's leg gave way and Barron touched Palmer for a sack.
Stanton went 2-1 as a starter earlier this season when Palmer was out with a damaged nerve in his throwing shoulder.
"Everyone has confidence in Drew," Arians said. "Nothing drops off."
On Peterson's second interception, the ball bounced off the hands of the Rams' Kenny Britt. Peterson caught it and raced to the end zone for the score. On St. Louis' next possession, Kareem Martin hit Davis and the ball came free as he tried to pass. Cromartie picked it up and ran in for the score to put Arizona up 31-14 with 3:58 to play.
Arizona has outscored opponents in the fourth quarter 91-34.
"I think we learned today that this game is four quarters long," St. Louis coach Jeff Fisher said. "Three doesn't get it done for you."
The Rams pointed to a crucial penalty after a 41-yard pass to Jared Cook had put the ball on the Arizona 4-yard line late in the third quarter. But Lance Kendricks was called for a blindside block, a 15-yard penalty that pushed St. Louis back to the Cardinals 45. Calais Campbell's second sack of the game eventually pushed the Rams out of field goal range.
"I thought it was a clean hit," Kendricks said.
Cook got behind rookie Deone Bucannon for a 59-yard touchdown pass with 1:50 left to give St. Louis a 14-10 halftime lead.
The Cardinals had scored 10 in a row to take the lead when Chandler Catanzaro tied an NFL record with his 17th consecutive field goal. The streak ended when he missed a 53-yarder the play after Palmer was hurt.
Arizona had six sacks after getting eight in its first eight games. ... The Cardinals have 14 interceptions and a plus-12 turnover ratio. ... St. Louis lost safety Lamarcus Joyner in the first half to a groin injury. ... Fitzgerald moved ahead of Keenan McCardell on the career receptions list and passed Michael Irvin for 24th in career yards receiving.
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