HOUSTON (AP) -- Playing in an NFL game was new to St. Louis Rams rookie quarterback Ryan Fitzpatrick. Coming back from a 21-point deficit wasn't.

The Rams' third-stringer took over for injured backup Jamie Martin on Sunday and then threw a 56-yard touchdown pass to Kevin Curtis in overtime to cap an improbable comeback and give the Rams a 33-27 win over the Houston Texans.

The seventh-round pick from Harvard stayed calm by thinking back to his freshman year and first college start when he rallied the Crimson from a 21-0 halftime deficit for a 31-21 win over Dartmouth. At the time it was the biggest comeback in Harvard's 128-year history.

"I was actually thinking about that game," Fitzpatrick said. "The biggest thing when you're in those situations is you need to get everyone around you fired up."

Houston (1-10) got the ball first in overtime but had to punt it away when David Carr was sacked on third down.

St. Louis (5-6) scored 10 points in the final 30 seconds of the game to force overtime.

"I knew there was no way we were going to lose that game," Fitzpatrick said. "You sort of get that feeling out there, of invincibility, with the way the offense was playing late and the way the defense really stepped up."

Isaac Bruce scored on a 43-yard pass with 26 seconds left and the Rams recovered an onside kick on the ensuing kickoff. Torry Holt caught a 19-yard pass to set up Jeff Wilkins' 47-yard field goal that tied it at 27 with four seconds left.

The Rams recovered from a horrible first half, with just 117 yards and six first downs, to gain 312 yards and 16 first downs in the second half.

Fitzpatrick proved an able replacement after backup Martin left late in the first quarter with a blow to the head. He was 19-of-30 for 310 yards and three touchdowns in three quarters, despite being sacked five times.

The Rams entered the game without starter Marc Bulger, who is out indefinitely with a shoulder injury.

Houston piled up 24 first half-points but fell apart in the second half, only adding a field goal the rest of the game.

"I felt sick out there," said Texans center Steve McKinney. "I was so disgusted I wanted to throw up. We were squandering some opportunities and sure enough it came back to bite us. It's really hard to lose a game when you're up 10 points with 30 seconds to go -- but we did."

The Texans missed a 46-yard field-goal attempt in the third quarter and earlier in that period safety Marcus Coleman intercepted a pass from Fitzpatrick but fumbled as he tried to return it. The Rams recovered and scored a touchdown three plays later.

Carr threw for a season-high 293 yards and three first-half touchdowns but couldn't find the end zone after that.

Andre Johnson had 159 yards, also a season high, and a touchdown. It was his first 100-yard game and first touchdown catch of the season.

Carr hadn't thrown more than one touchdown pass in a game in almost a year. So when he threw his third of the first half, a 10-yarder to Corey Bradford just before halftime, he was so jubilant that he chased Bradford down and wrapped him up before playfully tackling him in the end zone.

That jubilation was short-lived, however, as the Texans found a new way to lose this week, squandering their biggest lead of the season on Sunday.

Early in the game Carr had his way with a secondary that was missing both its starting cornerbacks and its strong safety.

Fitzpatrick's performance is even more impressive considering that the Rams played the entire second half without Pro Bowl left tackle Orlando Pace, who left the game in the second quarter with a hamstring injury.

"It was a great win playing a rookie secondary, a rookie quarterback and a makeshift offensive line," interim coach Joe Vitt said. "It wasn't pretty, but we got it done."

Holt scored on a 19-yard touchdown pass in the third quarter and Steven Jackson got the Rams within seven points on a 1-yard run midway through the fourth.

Jackson finished with 25 carries for 110 yards, improving the Rams' record when having a 100-yard rusher to 38-0 since moving to St. Louis in 1995.

Holt finished with 10 receptions for 130 yards and Bruce had four receptions for 94 yards. A 20-yard reception by Bruce late in the second quarter made him the 11th player in NFL history to top 12,000 yards receiving.

Game notes

The Texans' seven sacks was a team record. Linebacker Morlon Greenwood had two, a career high. ... Martin had blurred vision after being sacked by DaShon Polk. He made a quick trip to the hospital during the game and was scheduled to have more tests on Monday.