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CHAMPAIGN, Ill. (AP) -- Rex Grossman was having fun again.

The first-round draft pick drove Chicago 50 yards in the final 2:39 to set up Paul Edinger's 38-yard field goal as time expired as the Bears beat the Indianapolis Colts 20-18 on Saturday night in the preseason opener for both teams.

Grossman, who left Florida early after a disappointing junior year, was 9-of-21 for 74 yards -- including a 12-yard completion to rookie Bobby Wade on fourth down during the game-winning drive.

"That last drive was fun," he said. "I can't say everything else was exactly the way I wanted it to go. I think I got good experience out of it. Hopefully I'll be better next week.

Grossman thrived running Florida's Fun 'N' Gun offense under Steve Spurrier and was a runner-up for the Heisman Trophy in 2001. Things went sour, though, when Spurrier left for the NFL.

A year later, and Grossman was gone too.

The Bears aren't asking Grossman to do too much too soon.

Barring injuries, he'll spend the season as the third-string quarterback behind Kordell Stewart and Chris Chandler.

"We really couldn't have scripted it much better for Rex," Bears coach Dick Jauron said. "I thought he responded really well. When he do to, he put the ball on the money -- sometimes under duress. He certainly doesn't seem like a guy that panics at all."

It was also the Bears debut of Stewart, who signed with Chicago in the offseason after losing his job in Pittsburgh. The Bears gave Stewart every opportunity to show off his running ability and his arm on their opening drive.

The results were mixed.

Stewart completed his first pass over the middle for a 6-yard gain, then scrambled for 9 yards -- sidestepping linebacker David Thornton near the line of scrimmage to give Chicago a first down.

Two plays later, Stewart threw a short pass up the right sideline that was well short of his receiver. It was nearly intercepted as it sailed through the hands of defensive back Walt Harris.

In his final series, Stewart was sacked again on third down by Montae Reagor and fumbled. Brad Scioli recovered at the Bears 9, and Brett Conway kicked a 24-yard field goal to tie it at 3.

Stewart was 7-of-8 for 29 yards and played the entire first quarter before giving way to Chandler.

"It was exciting. It was different," Stewart said. "With the first game and everything, sometimes you don't see everything you need to see."

Indianapolis starters Peyton Manning and Edgerrin James both played two series before calling it a night. Manning was 4-for-7 for 36 yards, and James rushed for 13 yards on four carries.

Indianapolis missed three field goals, two by Mike Vanderjagt.

The Colts grabbed an 18-17 lead with 3:54 remaining when rookie Aaron Moorehead made a leaping touchdown grab and Brian Allen ran up the middle for a two-point conversion.

"We didn't really want the game to go into overtime," Colts coach Tony Dungy said. "If you don't get it, we've got to get the ball back, so it's a chance to practice that. If we do get it, it's a chance to practice our two-minute defense."

The Colts got that chance, but didn't like the results.

Grossman converted two fourth-down plays and was 5-for-10 for 39 yards during the game-winning drive.

Edinger also had a 29-yard field goal in the first half set up by a two long runs by Adrian Peterson.

The second-year running back had back-to-back runs of 15 and 14 yards to put the Bears in field-goal position before Stewart was sacked by Reagor for a loss of 6 yards on third and short.

Peterson, starting in place of Anthony Thomas, had 36 yards rushing on six carries.

Chandler capped an 11-play, 78-yard drive in the second quarter with a 22-yard touchdown pass to Ahmad Merritt. The Bears' backup was 5-of-10 for 48 yards.

Colts quarterback Jim Kubiak was 12-for-20 for 121 yards. He led the Cots to their first touchdown on a 10-yard pass to Williams, but also threw an interception that the Bears ran in for a touchdown to take a 17-10 lead.

Kubiak avoided a blitzing Joe Tafoya near the goal line and tried the heave the ball out of bounds but didn't get nearly enough on the throw. Todd McMillon picked off Kubiak's floating pass near the sideline at the 24 and jogged in untouched for the score.

"We probably weren't as sharp as I would like to be, but I saw some good energy and some positive things," Dungy said.

Colts backup running back James Mungro left the game in the second quarter because of bruised ribs. He was injured on a 14-yard run up the middle and rushed for 17 yards on four carries.

The Bears lost second-string offensive tackle Terrance Metcalf to a broken finger on his left hand.