With the league's longest active playoff drought hanging over them, the Buffalo Bills are far from content with their 2-0 start.

The Bills enter Sunday seeking their longest win streak since last opening 3-0 in 2011 as they host the San Diego Chargers, who won't have Ryan Mathews available for the foreseeable future.

Buffalo has made strides toward returning to the postseason for the first time since 1999, but its players see plenty of ways to improve.

Performing better in the red zone is one of them. The Bills are tied with New Orleans for an NFL-best 10 drives inside their opponents' 20-yard line but have scored three touchdowns.

They got one TD in six trips to the red zone last Sunday in a 29-10 victory over Miami, and Dan Carpenter matched a career high with five field goals in six attempts. Buffalo settled for a field goal in its only red-zone trip of the second half in a 23-20 overtime victory over Chicago to open the season.

"It's sad to just be kicking field goals. That's something we have to fix," said rookie Sammy Watkins, who had eight receptions for 117 yards against the Dolphins.

Watkins had the Bills' lone offensive touchdown -- the first of his career on a 12-yard catch -- as special teams played a major role. Besides getting C.J. Spiller's 102-yard kickoff return for a TD, Buffalo blocked a punt and recovered a muffed punt.

"How we played (Sunday) won't win for us later in the season," guard Chris Williams said.

The Bills, though, have played fairly well defensively. They've forced five turnovers and totaled six sacks while ranking fifth against the run, allowing 83.0 yards per game, after finishing 28th last year (128.9).

That's helped make up for an offense which has been limited to 28 first downs -- second-fewest in the league -- as E.J. Manuel has thrown for just 375 yards. However, he's thrown only one interception and been sacked once after being picked off nine times and sacked 28 in 10 games during his 2013 rookie season.

"You're never going to be perfect, but the good thing is we're still coming out with two wins versus two great teams," Manuel said. "As long as we win, I'm happy."

Buffalo has a recent history of turning promising starts into distant memories. The Bills lost 10 of 13 after winning their first three games in 2011 and began 4-0 in 2008 before dropping nine of 12.

"To sit here and say, 'Oh, did we expect to have people give us credit?' Not when you haven't done anything for such a long period of time. I think we understand that," coach Doug Marrone said. "We've got to get better each week. ... And really, all of our focus right now is the game that's next, San Diego."

The Chargers (1-1) head into Buffalo after holding off Seattle 30-21 last Sunday, beating the reigning Super Bowl champion despite Mathews being removed on a cart in the fourth quarter. San Diego announced Monday that he had a sprained right MCL but didn't disclose the degree of the injury or how long he would be out.

Mathews played in all 16 games for the first time in his four NFL seasons in 2013 and rushed for a career-high 1,255 yards.

"Everyone recovers differently," coach Mike McCoy said. "... We've had players who were supposed to be done for the season and the next thing you know they come out there Monday or Wednesday and they're practicing with something torn or something broken or this or that. I don't want to put a timetable on anything."

Danny Woodhead, Donald Brown and rookie Branden Oliver are the potential replacements for Mathews.

"We've said that we're going to play all our backs, certain rotations, certain number of plays," McCoy said. "... We have confidence in all our players. That's why they're here."

Mathews' injury could mean San Diego will look more to Philip Rivers and tight end Antonio Gates to keep their connection going from last week. Gates matched a career high with three touchdown catches and was named AFC offensive player of the week.

The 12-year veteran, among the league leaders with 13 receptions and 177 yards, has four TDs in four career games against Buffalo and had two in the most recent matchup, a 37-10 win in 2011.

The Bills have allowed their first two opponents to throw for a combined 590 yards, and the opposing tight ends caught 16 passes.