Arizona, the NFC West leaders, looked as if it had taken the lead late in the quarter when safety Antrel Rolle picked off a pass by Shaun Hill and returned it for a touchdown. But Arizona's Adrian Wilson was flagged for an offside penalty.

Wilson's reprieve came two plays later, when Hill fumbled the snap and Arizona's Clark Haggans recovered at the 49ers' 10-yard line with 38 seconds to go in the quarter.

Arizona trailed 21-13 at halftime, but then Warner heated up. The Cardinals opened the second half with a masterful seven-play, 61-yard touchdown drive.

Warner completed all six of his passes on the drive and accounted for every yard. His last pass was a 5-yard touchdown strike to Larry Fitzgerald on fourth-and-inches.

That cut Arizona's deficit to 21-20. The 49ers answered with a nine-play, 33-yard drive that ended with a 41-yard field goal by Joe Nedney.

Warner came right back, hitting Anquan Boldin for 17 yards and completing his next three passes. But the drive stalled at midfield, and the Cardinals were forced to punt.

Hill threw two second-quarter touchdown passes as the 49ers took a 21-13 halftime lead.

San Francisco coach Mike Singletary benched quarterback J.T. O'Sullivan in place of Hill, a journeyman making his third start, and first on the road, in seven NFL seasons.

Hill immediately made an impact.

With San Francisco leading 7-3 early in the second quarter, Hill threw a 31-yard touchdown pass to Josh Morgan, who beat Arizona cornerback Roderick Hood on the right sideline. Hood was flagged for holding on the play, but he couldn't stop Morgan, who briefly juggled the perfectly thrown ball before pulling it in and waltzing into the end zone.

That gave the 49ers a surprising 14-3 lead.

Hill led San Francisco on a 14-play, 77-yard drive, that he capped by hitting Vernon Davis for an 18-yard score with 29 seconds left in the half. Davis grabbed the pass over Wilson's head and the 49ers led 21-13.

Arizona trailed 14-3 in the second quarter when Warner went to work from his own 20.

Warner hit Steve Breaston for 18 yards, then found Breaston down the middle for 46 yards, setting the Cardinals up at San Francisco's 14.

One play later, Warner hit Boldin for a 13-yard touchdown to cut San Francisco's lead to 14-10. Boldin, who missed two games after a vicious hit by Eric Smith of the New York Jets in September, has caught a touchdown pass in six straight games, a team record.

The Cardinals added a 33-yard field goal by Neil Rackers later in the second quarter.

Arizona's rare "Monday Night Football" appearance had been billed as the Cardinals' chance to shed their image as longtime losers. It started on a horrible note.

San Francisco's Allen Rossum returned the opening kickoff 104 yards for a touchdown. He took the opening kickoff four yards deep in the end zone, broke through the first wave of tacklers and sailed untouched down the left sideline.

It was the fifth career kickoff return for a touchdown by Rossum, who has been bothered by a hamstring injury.

It was a yard shorter than the longest kickoff return in San Francisco history - a 105-yarder by Abe Woodson against the Los Angeles Rams in 1959.

Just like that, the Cardinals found themselves in a hole.

Arizona answered with a nine-play, 65-yard drive that resulted in a 28-yard field goal by Rackers to cut San Francisco's lead to 7-3.