Texans coach Bill O’Brien believes he finally has his franchise quarterback after going 9-7 with a revolving door at the position his first two seasons.

Andrew Luck is healthy, and the Colts’ challenge is keeping him that way all season.

Blake Bortles has much more help in Jacksonville, while Marcus Mariota may have the one of the NFL’s best backfields in Tennessee.

One of the NFL’s worst divisions in recent years, the AFC South now is filled with teams sensing huge opportunity this season thanks to all the young quarterbacks.

“It’s time for us to go out and prove we’re going to be a tougher division and go out and dominate our division,” Titans defensive tackle Jurrell Casey said. “That’s what we’re going to try to do.”

Indianapolis’ grip on the division slipped in 2015 with Luck missing nine games because of a variety of injuries. Houston slipped by the Colts to win the AFC South title at 9-7 despite playing four quarterbacks. The Texans then lured Brock Osweiler away from Denver with a four-year, $72 million contract, hoping to settle down the quarterback spot for O’Brien.

The Jaguars and Titans are very happy with their young quarterbacks, and Jacksonville owner Shad Khan has spent more than $350 million over the past two years to restock the roster for a team whose 19 victories since 2010 are the fewest in the NFL. Tennessee hired a new general manager and gave the coaching job to Mike Mularkey on a permanent basis, hoping to build on Mariota’s rookie season.

Here are some things to know about the AFC South:

ANOTHER TEXANS QB: Houston believes it saw enough to justify signing a quarterback with only seven career starts — all of them last season with Denver. Osweiler stepped in when Peyton Manning was injured and threw for 1,967 yards and 10 touchdowns before being benched for Manning in the season finale.

The Texans defend the division title with new running back Lamar Miller, who averaged 4.5 yards per carry last season in Miami, to replace Arian Foster. They drafted wide receivers Will Fuller and Braxton Miller to help DeAndre Hopkins. But rookie center Nick Martin will miss the season after ankle surgery, and left tackle Duane Brown remains on the physically unable to perform list. J.J. Watt, the three-time Defensive Player of the Year, also is recovering from groin surgery.

CHA-CHING JAGUARS: Khan has been shelling out big bucks for lots of free agents over the past two offseasons such as defensive tackle Malik Jackson, safety Tashaun Gipson and cornerback Prince Amukamara, all new this year. New defensive coordinator Todd Walsh also has defensive end Dante Fowler available after a knee injury wiped out his rookie season, and rookies Jalen Ramsey and Miles Jack join what could be a loaded defense.

The Jaguars have reworked their offensive line, including signing left tackle Kelvin Beachum, to better protect Bortles who was sacked 51 times in 2015. Bortles also has to take better care of the ball after leading the NFL with 18 interceptions to go along with his 35 TD passes.

COLTS: Coach Chuck Pagano has a new contract and a new defensive coordinator. Now he has to hope Luck stays on the field. Luck also has to play better after having almost as many interceptions (12) as touchdowns (15) in the seven games he played last season.

The Colts are going with a so-far impressive rookie at center in first-round pick Ryan Kelly, and a knee injury could keep left guard Jack Mewhort out for the next month. Injuries have hit the defense, too, forcing Indianapolis to sign veteran cornerback Antonio Cromartie.

Indianapolis also is depending on running back Frank Gore, 33, and outside linebacker Robert Mathis, 35, for veteran leadership and production.

RUNNING TITANS: Mariota turned in some dazzling moments as a rookie, but he missed four games because of sprained knees behind a line that gave up the most sacks (54) in the NFL. Tennessee revamped its offensive line yet again by signing center Ben Jones away from Houston and putting Jack Conklin, the eighth pick overall from Michigan State, at right tackle.

Mularkey wants to run to help the young QB. New GM Jon Robinson traded for DeMarco Murray in March, and the 2014 Offensive Player of the Year looks rejuvenated in Mularkey’s offense. An offense that hasn’t had a running back go for 100 yards in the last 32 games also has Heisman Trophy winner Derrick Henry as insurance.

PREDICTED ORDER OF FINISH: Texans, Jaguars, Colts, Titans.

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Online:

AP NFL website: www.pro32.ap.org and AP NFL Twitter feed: http://twitter.com/AP—NFL

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Follow Teresa M. Walker at www.twitter.com/teresamwalker