San Diego's chances for a fourth consecutive AFC West title looked slim, at best, following its home loss to Denver last month.

However, the Chargers are undefeated since then and back in the hunt for the divisional crown while the Broncos are falling fast since their 6-0 start.

San Diego looks to win its fifth straight and move into sole possession of first place in the West on Sunday when it faces a slumping Denver team that could be without its starting quarterback.

With a 34-23 loss to the visiting Broncos on Oct. 19, the three-time defending AFC West champion Chargers (6-3) fell 3 1/2 games behind Denver for the division lead.

San Diego quarterback Philip Rivers acknowledged it would be tough to catch up, but the Chargers have done so remarkably quickly. They've beaten Kansas City, Oakland, the New York Giants and Philadelphia over the last month to move into a first-place tie with Denver (6-3).

"We didn't know it would happen like this, or this fast, that we would be sitting here with the same record, but we believed we could get ourselves back in it because we were talking about 11 more ballgames," Rivers said after completing 20 of 25 passes for 231 yards and two touchdowns in last Sunday's 31-23 victory over the Eagles.

The Chargers' last four-game winning streak was over the final four games of last season, which they finished 8-8. San Diego became the first team to go from 4-8 to the playoffs with a 52-21 victory over Denver in the regular-season finale.

The Broncos lost their final three games in 2008, becoming the first team since divisional play started in 1967 to fail to make the playoffs after holding a three-game lead with three games left.

With a fourth straight defeat Sunday, Denver would drop in the division standings and move closer to missing the playoffs for the fourth straight season. Only two teams in the Super Bowl era have failed to advance to the postseason after opening 6-0.

"Crisis? No. Tough spot? Absolutely," Broncos safety Brian Dawkins said after Sunday's 27-17 loss at Washington. "You can't sit there and dwell on the piddly-poo of tears and worry about the last game. You have to move forward and that's what we're going to do."

The Broncos, though, may have to push ahead without starting quarterback Kyle Orton, who left Sunday's game at the end of the first half with a sprained left ankle.

"I was hoping to come back out and I just wasn't able to," said Orton, who completed 11 of 18 passes for 193 yards and two TDs to Brandon Marshall. "So hopefully I'll be able to go next week."

Backup Chris Simms, however, took the snaps during practice Wednesday and Thursday, making it increasingly likely he'll start. Making his first appearance of the season after Orton got hurt Sunday, Simms was 3 of 13 for 13 yards with an interception.

Simms hasn't started since Sept. 24, 2006, when he played for Tampa Bay and was battered so badly by Carolina that he needed emergency surgery to remove his spleen.

"His outlook, I'm sure, was probably affected by that, and I think he enjoys every day that he's here and he takes advantage of it," coach Josh McDaniels said. "That's why our team embraces him in his role and would embrace him in whatever role he would serve for us."

While Denver looks to improve an offense that had just 36 second-half yards last Sunday, the Broncos might also need to work on defending the run.

After Denver allowed 79.7 rushing yards per game during its 6-0 start, opponents are averaging 157.3 yards on the ground versus the Broncos in the last three weeks.

That could be good news for Chargers running back LaDainian Tomlinson, who rushed for a season-high 96 yards and two TDs last week.

After learning before the game that his wife LaTorsha was pregnant with the couple's first child, Tomlinson moved into 12th-place all-time with 12,145 rushing yards and third all-time with 146 touchdowns, trailing Hall-of-Famers Jerry Rice and Emmitt Smith.

"I grew up watching all those guys," said Tomlinson, who carried 18 times for 70 yards last month versus Denver. "It's mind-boggling that I am third all-time."

Sunday marks San Diego's first visit to Denver since a controversial 39-38 loss on Sept.14, 2008. Two plays after referee Ed Hochuli incorrectly ruled Jay Cutler's lost fumble was an incompletion, the former Broncos quarterback found wide receiver Eddie Royal for a four-yard TD on fourth down with 24 seconds left. Royal caught the ensuing two-point conversion.

In last month's victory in San Diego, Royal became the first Bronco to return a punt and a kickoff for a touchdown in the same game.

Chargers running back Darren Sproles returned a punt 77 yards for a score in that contest.