After riding shotgun to Peyton Manning's high-octane offense all of last year, Denver's defense had the five-time MVP's back for once.

Rookie Bradley Roby broke up Andrew Luck's fourth-down pass to Reggie Wayne just after the 2-minute warning Sunday night, preserving Denver's 31-24 nail-biter over the Indianapolis Colts.

"We said we've got to make a play to win the game," Roby said. "We can't rely on the offense. It's on us."

The Broncos were clinging to the last wisps of what seemed like a safe 24-0 lead when the first-round draft pick from Ohio State sliced in front of Wayne to knock away Luck's pinpoint pass.

"I kind of felt like they were going to come at me, just being a rookie, going against their best receiver," Roby said. "He kind of got me off the line, but just thankfully, I was able to recover and make the play at the end."

On the sideline, Manning and tight end Julius Thomas, who hooked up for three first-half touchdowns, cheered.

"Thank goodness our defense came up with some big stops," said Manning.

He blamed the second-half sloppiness on opening night jitters.

GM John Elway spent more than $100 million on a defensive makeover in the offseason, trying to toughen up his team after its Super Bowl shellacking at the hands of Seattle. Then, he grabbed Roby in the first round of the draft. Add in several starters who were returning from injuries and Denver's defense spent all summer trying to develop a new, nasty identity.

Although Luck engineered four second-half scoring drives, the Broncos, who watched footage of the old "Orange Crush" defense during the week, had their moments.

Denver's defense came up with two big stops deep in its territory during a third quarter dominated by Indy. On fourth down at the 1, Marshall stuffed Luck's run up the middle. Then, when the Colts had a first down inside the 5, the Broncos held them to Adam Vinatieri's 25-yard field goal following DeMarcus Ware's third-down sack.

"It wasn't the best win, but guess what, it was a great opener," said DeMarcus Ware, who had 1 1/2 sacks in his Denver debut after franchise-high 117 in nine seasons in Dallas.

Brandon Marshall, filling in for Danny Trevathan (leg), led the team with nine tackles in his first NFL start, and Roby tied newcomer Aqib Talib with three pass breakups.

"At the end of the day, we made the right play at the right time," said Rahim Moore, who had a career-best two interceptions in his first game since undergoing emergency surgery on his left calf in November.

Other takeaways from Denver's win, which snapped a six-game skid against the Colts:

THOMAS' TRIO: Thomas beat a linebacker on each of his first two TDs, outmuscling one on a 3-yard crossing route and outracing another on a 35-yard TD. Then, he slipped inside the safety for his third score, which tied Shannon Sharpe's franchise record for TDs by a tight end in a game.

"Something I pride myself on is being ready for man coverage," Thomas said. "It's like backyard football with your little brother or cousins. I don't believe you should be covered 1-on-1."

WELKER'S SUSPENSION: With the game's premier slot receiver, Wes Welker, serving a four-game suspension for violating the NFL's policy on performance-enhancing drugs, the Broncos couldn't convert third downs, going 1 for 7 in the second half after a first half in which they went 6 of 7.

"We've got to find a way to play all four quarters as an offense," Manning said. "Thank goodness the defense picked us up when the offense wasn't doing their job quite as well."

Fox said he never found himself wishing he had Welker in certain situations.

"To be honest with you, it never crossed my mind," he said.

MOMENTUM CHANGER: Luck's 9-yard scamper into the end zone with 19 seconds left in the first half not only got the Colts on the board by halftime but it turned the tide.

"We did manage to take advantage of some opportunities in the second half that we didn't in the first," Luck said. "It was good to get that two-minute drive right at the end of the half."

A 24-point deficit proved one touchdown too many, though.

"Obviously, when you start the way that we started, you dig yourself a hole you can't come back from," Colts coach Chuck Pagano said.

Notes: Manning's win over his former team means he and Brett Favre are the only QBs to have beaten all 32 current NFL teams. "I think it means you have to be old," Manning said. ... RB Ronnie Hillman and CB Kayvon Webster, who had to stay behind in Dallas last week after falling ill during the final preseason game, were both inactive. Fox said they just fell behind in the game plan. ... Two Colts LBs were hurt: Cam Johnson (triceps) and LB Jerrell Freeman.

___

AP NFL website: www.pro32.ap.org and www.twitter.com/AP_NFL