INDIANAPOLIS (AP) - Andrew Luck knows life in the NFL can't be this easy for a rookie.

The No. 1 overall draft pick threw his first NFL pass for a long touchdown, just like Peyton Manning in 1998, then led Indianapolis to two more touchdowns. Luck one-upped his predecessor by winning Sunday's preseason opener 38-3 over St. Louis - Indy's first preseason-opening win since 1994.

"To get a win, get in the game and put some drives together is great," Luck said. "But I realize, and the guys in the locker room realize, it's a preseason game and things will be different as the season goes along."

Luck might have the toughest job in football this season - replacing Manning, the longtime face of Indy's franchise.

But he showed everyone Sunday that he can do whatever is asked.

Colts coaches wanted the man billed as the most polished NFL rookie since Manning to take 20 to 25 snaps. He got 24.

They wanted to keep him upright, and though Luck hit the ground twice, he was not sacked.

They wanted him to show his command of the offense, and in less than one half, Luck seemed to have Manning's playbook down pat, from the perfect baseball slide to rushing his team to the line of scrimmage so the Rams couldn't challenge a catch on the sideline.

The rookie quarterback wound up 10 of 16 for 188 yards with two TD passes and a quarterback rating of 142.6. Three of the incompletions were drops, two were throwaways, and only one pass, the deep out that rookie T.Y. Hilton barely caught on the sideline, came close to being picked off. It was the most lopsided preseason win for the Colts (No. 32 in the AP Pro32) since a 35-0 rout of Washington in 1966.

"I know we picked him up off the turf a couple times, but he's a big, strong, athletic guy and he can take a hit. We don't want him taking too many, but to see him perform the way he did and do the things that he did under pressure, I thought he handled it well," new coach Chuck Pagano said.

After everything the Colts endured during the run up to drafting Luck - the injury to Manning, an 0-13 start in 2011, the release of many fan favorites including Manning during a tumultuous offseason - Luck quickly turned the page on the past with a start fans may never forget.,

With the rookie quarterback under pressure on his first play, Luck calmly stepped forward and dumped the ball off to Brown, who darted up the field with blockers in front, then cut from right to left and outran the defense to the end zone. Luck pumped his fist in the air and jogged to the sideline with a broad smile across his face.

Longtime Colts fans had seen it before. Back in '98, Manning's first pass was an 8-yard route to Marvin Harrison, who took the ball and sprinted to the end zone for a 48-yard score.

"I think (quarterbacks coach) Clyde (Chirstensen) told me that about a week ago," Luck said, laughing. "I guess it's coincidence. Funny, huh?"

Certainly not to the Rams (No. 28), who pressured Luck most of the day, yet couldn't force him into mistakes, get him on the ground or find a way to reach the end zone.

The Rams' offense moved the ball on its first two series, under Sam Bradford, but stalled. St. Louis did get a 37-yard field goal when Kellen Clemens was running the offense.

Otherwise, it was a daylong struggle for Jeff Fisher's new team.

"It's kind of an unusual game because the offense puts a drive together and then, bang, they're back on the field one play later because we gave up a touchdown," the Rams coach said. "Then you're trying to catch up with plays for your defense and then you can't stop them and then you can't get the plays for your offense. We tried to get as many plays as we could on tape and we'll move on."

Bradford, the No. 1 overall pick in 2010 and the Offensive Rookie of the Year, was 7 of 9 for 57 yards and recovered his own fumble. Clemens was 4 of 6 for 18 yards.

And the feature attraction stole the show.

"He's a good player. He's got mobility and he sees well," Fisher said of Luck. "He has got arm strength. Coach (Bruce) Arians has done a great job with him so this far in the offense."

And the Rams had no answers.

Four plays after converting third-and-3 with the 12-yard pass to Hilton, Luck hooked up with Austin Collie in the front corner of the end zone for a 23-yard score to make it 14-0.

On Luck's fourth series, he took the Colts on a methodical 13-play, 80-yard drive. Delone Carter ended the drive with a 1-yard run to make it 21-3, and Indy closed it out with two second-half touchdowns and Pat McAfee's 31-yard field goal - even if the Colts know things are about to get much tougher for the rookie.

"I'm sure he's going to have some bumpy roads from here on out. Every game is not going to be like this," veteran receiver Reggie Wayne said. "As players, we understand that. Us being able to overcome those bumpy roads and keep it moving makes the next time out there better."

Notes: The Colts lost four players to injury. Linebacker Pat Angerer (foot), starting offensive guard Mike McGlynn (sprained ankle), linebacker Scott Lutrus (sprained knee), and Carter (ribs) all left the game early and did not return. ... St. Louis played without receiver Danario Alexander (hamstring) and defensive tackle Trevor Laws (leg). ... The Rams ran 32 times for 116 yards, a 3.6-yard average. Isaiah Pead had 10 carries for 33 yards.

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