With their franchise quarterback out for the season, the New England Patriots have patched together a successful start to 2008.

The San Diego Chargers have no such excuse, yet they own a losing record.

To avoid falling into a deeper hole, the Chargers must try to beat a Patriots team looking for its second straight win in California when these traditional AFC powers meet on Sunday night.

It's been a topsy-turvy start to the season in the AFC, where the Chargers, Patriots and Indianapolis Colts have combined for 11 division titles in the last four years. None of those elite teams currently leads its division, and only New England sports a winning record.

The Patriots have managed to start 3-1 despite losing Tom Brady to a season-ending knee injury in the first quarter of their Week 1 game against Kansas City. With backup Matt Cassel passing for a career-high 259 yards last Sunday, New England bounced back from a loss to Miami before its bye week, winning 30-21 at San Francisco.

Randy Moss, who had only 47 receiving yards in his previous two games combined, exceeded that total on one play as Cassel hit the star wideout in stride for a 66-yard touchdown pass.

"Being able to connect on that deep ball, I think it was good," Moss said. "That's something that we've been missing in our repertoire the past couple of weeks."

Inconsistency continues to dog the Chargers (2-3), who are averaging 29.6 points to rank fourth in the league but have lost three games by a total of 10 points.

Quarterback Phillip Rivers is second in the AFC with 11 touchdown passes, but he's struggled recently. Over the past two games, Rivers has completed less than 51 percent of his throws for a total of 339 yards with two TDs and two interceptions while getting sacked six times.

San Diego recovered from a 2-3 start last season to win its second straight AFC West title, but the road appears tougher in 2008. After facing the Patriots, the Chargers travel to AFC East-leading Buffalo. Looming in two weeks is a trip to London to play the high-powered New Orleans Saints.

"Make no mistake about it: This is a critical time for our football team," San Diego's LaDainian Tomlinson said. "These next (three games) before the bye are very critical for us. To me, this is going to determine what type of team we're going to be this year."

Slowed by an injury to his right big toe, Tomlinson has run for only 331 yards through five games after rushing for more than 1,400 in each of the last three seasons.

He managed 35 yards on 12 carries last Sunday in a 17-10 road loss to the Dolphins and it was his third game this year without a touchdown, the same number of times that happened all of last season. Tomlinson had a chance to tie the game early in the fourth quarter, but Miami's defense stopped him on fourth-and-goal from the 1-yard line.

"We've been down this road and found a way to win these games in the second half," San Diego coach Norv Turner said. "But we weren't able to get it done (Sunday)."

Now, the Chargers face the team that eliminated them from each of the last two postseasons, including a 21-12 loss at New England in the AFC championship game Jan. 20. The Patriots also beat the Chargers 38-14 at Foxboro in Week 2 of 2007, part of their 13-3 edge in the all-time series including playoffs. San Diego must defy that history if it hopes to avoid its worst start since opening 1-5 in 2003 en route to a 4-12 finish.

"It's very critical, crucial, whatever you want to call it. To me, it's definitely a must-win for us," Tomlinson said.

The Patriots have spent the entire week in California after beating the 49ers. Instead of flying back to the East Coast, New England practiced at San Jose State during the week before making the trip south to San Diego.

"To play such a physical game, and a long and grinding game, and then have to fly back six hours to the East Coast, try to get yourself reacclimated and get some rest, then practice a few days and then fly right back, I thought that was the dumbest thing we could possibly do," veteran safety Rodney Harrison said. "It's really nice to be on a regular schedule. ... I'm 35 years old, so I need to feel as good as possible."

The win at San Francisco marked the Patriots' 12th straight regular-season road victory since a 21-0 loss at Miami on Dec. 10, 2006.

Cassel completed 22 of 32 passes against the 49ers, but also threw two interceptions and got sacked five times. A lack of mobility has plagued Cassel, who has been sacked 15 times -- tied for third-most in the NFL.