The Indianapolis Colts were expected to be the Houston Texans' most formidable challenger in the AFC South.

There hasn't been much of a challenge, but it's the Colts who are threatening to run away with the division.

The Colts will try to overcome the loss of Reggie Wayne when they head to Houston on Sunday night looking to all but end the Texans' hopes of a third straight division title by handing them a sixth consecutive loss.

Houston (2-5) edged Indianapolis (5-2) by one game for the South title last year, but what seemed like it would be a tight race in 2013 has been anything but.

As the only team in the division above .500, the Colts seem on their way to supplanting the Texans, who are facing a potential six-game slide for the first time since Nov. 6-Dec. 11, 2005.

Indianapolis, though, isn't getting caught up in Houston's recent struggles, which include averaging 12.2 points over the last five games.

"There's a saying -- to be the champ, you got to beat the champ. They're the champ," linebacker Robert Mathis said. "In order to get it back, we've just got to go down there and handle our business. I've been a part of some division championship teams. They're focused and they want it, it's just a matter of taking care of business.

"Make no mistake about it, we're not looking at their record because they are the two-time AFC South champions and we respect them as such."

The Colts are commanding respect of their own after defeating previously unbeaten Denver 39-33 in Week 7 to spoil Peyton Manning's return to Indianapolis before entering the bye.

Despite the impressive victory over the Broncos, the Colts suffered a costly blow as Wayne was lost for the season with a torn ACL in his right knee.

It's the first time since 2001 the Colts will put together a game plan without the three-time All-Pro. Darrius Heyward-Bey and T.Y. Hilton will be asked to do more, while tight end Coby Fleener may also see more passes from Andrew Luck.

Luck hit Heyward-Bey and Fleener for two of his three touchdown passes against the Broncos.

The second-year signal caller, who hails from Houston, will likely find things much tougher against the Texans. Though Houston is 27th in scoring defense (27.7 points per game) largely thanks to the offense and special teams allowing seven return touchdowns, the Texans are the league's top-ranked total defense, allowing an average of 267.7 yards -- 145.6 passing.

"They've got game-wreckers all over the place. They've got a front seven that is as good as anybody in football. They've got probably the best defensive player in football in J.J. Watt," coach Chuck Pagano said.

Luck should be well aware of Houston's impressive defense after he was sacked six times while the teams split two meetings last season. Five of those sacks -- three by Watt -- came in a 29-17 defeat at Reliant Stadium in Week 15, when Luck completed 13 of 27 passes for 186 yards and two touchdowns, including a 61-yard toss to Hilton.

Luck again won't have to worry about Brian Cushing, who torn his left ACL for the second straight season. The linebacker's latest injury came in a 17-16 loss at Kansas City in Week 7, giving the Texans the bye to prepare for the Colts.

"We had to adjust to that last year," coach Gary Kubiak said. "We'll have to do that again. J.J. is already a leader, but I think it's going to call for some other guys to be vocal. I think (middle linebacker) Joe Mays has got more confidence in what he's doing.

"Unfortunately, we've been down this road before and some guys will have to step up."

The same could be said for Case Keenum, who will make a second straight start in place of a healthy Matt Schaub.

Keenum completed 15 of 25 passes for 271 yards and a touchdown in his first NFL appearance against the Chiefs while Schaub was out with a foot injury.

Sticking with Keenum might be made easier since Schaub has been largely ineffective, compiling a 78.8 passer rating with eight touchdowns and nine interceptions -- four returned for TDs.

"I've got to make decisions I think are best for the football team right now," Kubiak said. "The decision I made was based on what I saw take place last week with Case and him taking advantage of an opportunity. I want to see him move forward."

The Colts rank 29th against the run, surrendering an average of 122.3 yards, but Houston's chances to take advantage might depend on the health of its two top backs.

Arian Foster has routinely shredded Indianapolis, gaining 752 yards while averaging 6.6 per carry with six touchdowns in five career meetings, but a hamstring injury limited him to four carries against the Chiefs. He didn't practice Wednesday and is considered questionable for Sunday.

Backup Ben Tate has a rib injury, but went through a light practice Wednesday and expects to play.