NASHVILLE, Tenn. -- After enduring losing seasons during his last two years at Kentucky, linebacker Avery Williamson came to the Tennessee Titans and promptly slogged through 2-14 and 3-13 seasons his first two years in the NFL.

After Sunday's 13-10 win over the Denver Broncos in Nissan Stadium that kept Tennessee in a first-place tie in the AFC South with Houston, Williamson could be excused for feeling like he had won the lottery.

"It seems surreal," Williamson said. "I was really questioning life, wondering why I was being stuck on bad teams. We've got the right people in the front office, a GM that's making moves, and players in here that really want to win."

Williamson did his part, as he was credited with forcing the game-deciding fumble from Denver tight end A.J. Derby with 53 seconds left after an 11-yard reception. Safety Daimion Stafford pounced on the ball at the Broncos' 40-yard line to seal the outcome.

It was the biggest play in a day of big plays from a defense which has been maligned at times because of its shortcomings in the secondary. After a 27-21 win at Chicago two weeks ago in which the Titans (7-6) nearly blew a 27-7 fourth quarter lead, they cut starting cornerback Perrish Cox.

The reconstituted secondary held its own against Broncos quarterback Trevor Siemian, who returned to the lineup after missing last week's 20-10 win in Jacksonville with a foot injury. Siemian completed 35 of 51 passes for 334 yards, but didn't hit anything deep and absorbed three sacks.

Brice McCain started in Cox's place and contributed three tackles, along with a pass defensed. Valentino Blake bagged six tackles and broke up a pass, while rookie LeShaun Sims notched five stops and broke up a potential touchdown pass on the fourth quarter's first play by knocking the ball out of Demaryius Thomas' arms in the end zone.

"The defense was tremendous," quarterback Marcus Mariota said. "This is part of the process."

The process included a lot of running against the NFL's 28th-ranked rush defense, as Tennessee finished with 180 yards on the ground, including 92 on 21 carries from DeMarco Murray. In fact, Murray accounted for the Titans' only touchdown by powering over from the 1 with 7:29 left in the first quarter, capping an 11-play, 70-yard drive on which nine of the plays were runs.

By contrast, Denver (8-5) didn't bother to establish a running game. Veteran Justin Forsett, picked up on Monday off the waiver wire, fumbled on his first carry and it led to a 53-yard field goal by Ryan Succop less than two minutes after Murray's score.

It was one of just nine running plays, good for a measly 18 yards, for the Broncos.

"We were playing catch-up, so we were throwing the ball a lot," Denver coach Gary Kubiak said. "Obviously, there wasn't much commitment to the run. We were trying to get back into the game throwing it a lot."

Succop converted a 41-yard field goal with 1:27 left in the first half for a 13-0 halftime lead. That finished a 19-play, 74-yard drive that chewed up 8:04. A Mariota touchdown pass to Rishard Matthews was nullified by Delanie Walker's second offensive pass interference flag of the half.

Tennessee did nothing offensively after halftime, Mariota completing just one pass -- a 26-yarder late in the fourth quarter to Matthews -- as he suffered through a 6-of-20 day for 88 yards. Its defense managed to hold off a patented Broncos' rally late.

Siemian found Emmanuel Sanders for a 3-yard touchdown pass with 9:58 left in the game, cutting Denver's deficit to 13-7. Brandon McManus hit a 34-yard field goal at the 4:28 mark to make it 13-10, and the Broncos got the ball back at their 2 with 2:26 and two timeouts left, plus the two-minute warning.

That's when Williamson and Stafford teamed up for the game-sealing play.

"It felt good," Stafford said of his fumble recovery. "We didn't have to go out there no more. We could go back inside where it's warm."

NOTES: ILB Brandon Marshall (hamstring) led the list of Denver inactives, which also included QB Austin Davis, WR Jordan Norwood, CB Lorenzo Doss, LS Casey Kreiter, G Connor McGovern and G Billy Turner. ... DT Jurrell Casey (foot sprain) was deactivated by Tennessee, as was WR Kendall Wright, who according to a report on Twitter was late and missed meetings on Saturday. The Titans also deactivated RB David Fluellen, DB Curtis Riley, LB Justin Staples, G Sebastian Tretola and TE Jace Amaro. ... Tennessee QB Marcus Mariota's first completion made him the franchise's first 3,000-yard passer in a season since Matt Hasselbeck (2011).