The Colts will be without Andrew Luck from two to six weeks with a lacerated kidney and torn abdominal muscle injured late Sunday in a win over Denver.
Luck's injury comes just as the Colts looked as if they were taking control of this division.
Now the Colts turn to Hasselbeck, hoping the veteran can keep them atop the AFC South until Luck returns.
''We've got all the confidence in the world in Matt Hasselbeck, and we're not going to put Andrew back out there until he's healed and ready to go,'' Colts coach Chuck Pagano said.
The AFC South is at risk of being only the NFL's third division since 1970 won by a team with a losing record. Carolina did it last season at 7-8-1 in the NFC South, and Seattle was 7-9 taking the NFC West in 2010.
This division is just 6-17 against anyone else, a mark bolstered by two wins over Tampa Bay.
The NFC West went 10-30 in 2008 for a .250 winning percentage for the worst divisional mark since 1970.
The 2014 NFC South was just behind at 10-29-1 (.263), according to STATS.
These AFC South teams were a combined 12-28 (.300) in 2013, tied for fifth-worst with the 2009 NFC West.
So the AFC South could be won by the first team with a winning streak in the second half of the season. Even the last-place Titans (2-6) are just 1 1/2 games back of the Colts, so everyone sees opportunity in this division.
''Go out there and control what we can control and see what happens,'' Houston defensive end J.J. Watt said.
Here are some things to watch out of the AFC South down the stretch:
COLTS ON TOP, FOR NOW: Indianapolis finally became the fourth AFC South team to win a game outside the division, and it was a doozy knocking off the previously undefeated Broncos 27-24 on Sunday. That win gave the Colts (4-5) a one-game lead in the division, but proved costly with Luck lost to injury again. Luck and the Colts get the bye this week as part of his recovery.
Hasselbeck put the Colts in control of this division when he filled in for Luck earlier this season, but he beat Jacksonville and Houston. The Colts' toughest remaining games come in the next month with trips to Atlanta and Pittsburgh wrapped around a home game against Tampa Bay. Those road games are against the only opponents currently with winning records left on the Colts' schedule.
TEXANS SHOWDOWN: The Texans have had so much more drama since wrapping the HBO series ''Hard Knocks'' going back and forth between starting quarterbacks before Ryan Mallett missed the team flight to Miami and was cut a couple of days later. They lost running back Arian Foster for the season to a torn Achilles tendon late in that ugly loss in Miami. But they went into their bye feeling better after beating up Tennessee's backup quarterback in a 20-6 win on Nov. 1. That left the Texans at 3-5.
TITANIC SKID: That loss in Houston cost Ken Whisenhunt his job as controlling owner Amy Adams Strunk watched the Texans sack Zach Mettenberger seven times. She fired Whisenhunt on Nov. 3 after a 3-20 tenure and promoted Mike Mularkey as interim coach. With rookie Marcus Mariota returning from a sprained MCL in his left knee, Mularkey protected Mariota and rewarded him with a 34-28 overtime win over New Orleans to snap a six-game skid.
That was the first in-season coaching change for veteran linebacker Brian Orakpo who called it a dreadful week for the Titans. The OT win gave them an emotional boost. ''To come out against a team like that that scores so many points and do what we did, it's huge,'' Orakpo said.
Now Mularkey's next challenge is snapping a home skid that has reached nine games since the previous win Oct. 12, 2014 - against the Jaguars.
CLOSER JAGUARS: Jacksonville beat in-state rival Miami, then rallied for a big win over Buffalo in London. But the Jaguars lost to Tampa Bay, and turnovers keep costing them chances at victories. If coach Gus Bradley can get them to quit hurting themselves, the Jaguars might have the easiest schedule left with Atlanta the only opponent with a winning record.
PREDICTED ORDER: Colts, Titans, Texans, Jaguars.
AP Sports Writers Michael Marot in Indianapolis, Kristie Rieken in Houston and Mark Long in Jacksonville, Florida, contributed to this report.
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Follow Teresa M. Walker at www.twitter.com/teresamwalker