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ST. LOUIS -- Sam Bradford missed high, low, left, right.

After capping the St. Louis Rams' opening drive with a touchdown pass to Lance Kendricks, the former No. 1 overall pick endured an 0-for-12 slump that included Patrick Peterson's interception in the end zone on a pass tossed up for grabs under heavy pressure.

No worries. The Rams' rapidly improving defense saw to that.

"Those guys played outstanding," Bradford said after the Rams knocked off the previously unbeaten Arizona Cardinals 17-3 on Thursday night. "They've played great all year and they have kept us in a lot of games."

Bradford busted out of his funk with a 51-yard touchdown pass to rookie Chris Givens for a two-TD cushion, and Robert Quinn had three of the Rams' nine sacks on Kevin Kolb to keep the Cardinals in check.

The Rams have three first-round picks on the defensive line and the fourth, tackle Kendall Langford, was a key free-agent pickup.

"We believe in ourselves," Quinn said. "We believe we can be one of the great defenses. When there was a play to be made, we made it."

Arizona (4-1) scored at least 20 points in each of its first four games, but had no luck containing a pass rush that had totaled just six sacks on the year, and got stopped twice inside the 20 in the final minutes. The Rams also had a strong defensive game last week in a 19-13 victory against Seattle, also at home.

Kolb got his helmet knocked off twice on hits, once after getting popped in the jaw. He described the Cardinals' first-half woes as "sickening."

"I'm all right," Kolb said. "I'm glad we've got the weekend to heal up, mentally and physically."

The Rams also limited the Cardinals to 45 yards rushing on 17 carries.

"Bottom line, they decided they wanted to throw the ball a lot and that made it kind of a track meet," Rams defensive end Chris Long said. "We've been waiting a long time to feel like we've done our job on defense."

Kendricks caught a 7-yard TD pass in the first quarter and Greg Zuerlein kicked a 53-yard field goal in the second quarter for the Rams (3-2), who are 3-0 at home and ended Arizona's seven-game winning streak in St. Louis -- the Cardinals' home before leaving for the desert in 1988.

"I didn't like anything," coach Ken Whisenhunt said. "The thing I respected is our guys didn't quit, and even as bad as it went, we had a chance at the end of the game."

The Rams totaled two victories last year but so far have executed a quick turnaround under new coach Jeff Fisher. They're 3-0 at home for the first time since 2003, when they were unbeaten in the Edward Jones Dome, and they're above .500 for the first time since they were 4-3 on Nov. 4, 2006.

"I've never been there before," Long said. "I'm unfamiliar with the sound of it, but I'm liking it."

Bradford finished 7 for 21 for 141 yards, the second-lowest total of his career. He threw for 126 yards against Tampa Bay his rookie year in 2010.

Before the second TD pass, he had been 3 for 16 overall for just 25 yards, often missing on his receivers by a lot. Undoubtedly, he missed Danny Amendola, sidelined in the second quarter with a right shoulder injury on a diving attempt that was initially ruled a 22-yard catch for a first down but overturned after the Cardinals challenged.

Amendola perhaps hinted at the extent of the injury when he flung his helmet, with his left hand, while walking in a tunnel to get X-rays. He had the arm in a sling after the game, but the Rams did not make him available to reporters.

Rams general manager Les Snead told ESPN.com's Jeffri Chadiha that the team won't know Amendola's diagnosis until Friday. Snead said Amendola's clavicle doesn't appear to be broken, and he expects him to be able to play again this season.

The Rams, ranked 27th in offense, came out throwing, with Bradford completing passes of 14 yards to Brandon Gibson and 44 yards to Amendola on the first two plays, setting up the score to Kendricks on third down. It was the first offensive touchdown in three games for St. Louis.

Arizona responded with a drive that lasted 9:24, ending with Jay Feely's 35-yard field goal. The Cardinals kept the drive alive with three third-down conversions. Larry Fitzgerald's 5-yard catch on the first play of the drive marked the 122nd straight game with a catch, a franchise record.

Zuerlein, a sixth-round draft pick out of Missouri Western, made it 10-3 early in the second quarter. He is 13 for 13 this season, including four kicks of 50-plus yards.

Feely missed a 40-yard field goal late in the second quarter.

Bradford was 3 for 4 for 65 yards on the opening drive before cooling off. St. Louis was well within Zuerlein's range at the Arizona 16 late in the third quarter when a pass was intercepted by Peterson in the back of the end zone.

Arizona's loss leaves Atlanta and Houston as the only remaining unbeaten teams. The Cardinals were still the St. Louis Cardinals the last time they were 4-0, in 1974. Known as the "Big Red," those Cardinals won their first seven that season en route to a 10-4 record, before losing in the first round of the playoffs to Minnesota.

The loss was only the Cardinals' third in 14 games since starting the 2011 season 1-6.

Game notes

Fitzgerald broke the mark set by Mel Gray from 1973-82 and finished with eight catches for 92 yards, leaving him 48 yards shy of 10,000 for his career. ... Kurt Warner, who took the Rams to two Super Bowls and the Cardinals to one, got a huge sustained ovation when he was introduced in the first quarter. Warner and another former Rams great, Marshall Faulk, are on the NFL Network broadcast team.

Information from ESPN.com's Jeffri Chadiha and The Associated Press was used in this report.