The Cardinals (7-1), who have sole possession of the best record in the NFC this late in the season for the first time since 1974, won their fourth straight, including back-to-back wins over the top two teams in the NFC East.
"This is a very good team," said Palmer, 5-0 this season after missing two games with a shoulder injury. "We feel like we can play with anybody, and that's important because we feel like we are improving."
Romo was out with his third back injury in 18 months, and backup Weeden threw two interceptions as the Cowboys (6-3) dropped their second straight. He finished 18 of 33 for 183 yards with a late score.
"You can't turn the ball over, and that is on me," Weeden said.
The Dallas running game wasn't the same without Romo.
NFL rushing leader DeMarco Murray's record streak of eight straight 100-yard games to start the season ended against a defense that didn't allow a back over the century mark for the 18th consecutive time.
Ellington outgained Murray on the ground with 95 yards and added another 39 receiving.
"You know we always want to outrush the opponent," Ellington said. "It's a credit to our defense for shutting him down and giving me a chance to get out there on the field and get more carries and get more yards."
Romo was relegated to headset-wearing sideline duty because of fractures of two small bones in the back. The injury is unrelated to a herniated disk sustained last year and to offseason surgery to remove a cyst earlier in 2013.
Coach Jason Garrett said Romo would make the long trip to London for next weekend's game against Jacksonville even though staying home would essentially give the 34-year-old a month between games because of a bye the following week.
"We're optimistic," Garrett said. "People with similar injuries have been on a little bit of a similar timetable where they missed the first game and they were getting close to being able to play in that second game."
Weeden, who left Cleveland when the Browns gave up on him just two seasons after drafting him in the first round, was off-target and out of sync with his receivers most of the game.
NOTES: Larry Fitzgerald extended the longest active streak with at least one catch to 157 games. He had a 31-yarder on third down on Arizona's first scoring drive while trailing 10-0 and led the Cardinals with five catches for 70 yards. ... The Cardinals beat the Cowboys for the fourth straight time, and this was the first that wasn't on the final play. Two of the previous three victories were in overtime. ... Cowboys LB Rolando McClain and DT Tyrone Crawford left the game in the fourth quarter with knee injuries.
Copyright 2014 by The Associated Press