Edwards went 25-of-30 for 261 yards and a touchdown, and Mitchell intercepted a pass from Philip Rivers at the goal line to thwart a potential go-ahead score midway through the fourth quarter to secure a 23-14 win Sunday.
Mitchell's interception allowed Edwards to engineer a seven-play, 43-yard drive to set up Rian Lindell's 44-yard field goal for a 23-14 lead with 3:17 remaining. Then Mitchell came through again, when he forced Rivers to fumble on San Diego's next possession.
Edwards hit Lee Evans on a 2-yard touchdown pass and Marshawn Lynch also scored for the AFC East-leading Bills, who are off to their first 5-1 start since 1995. Buffalo, off the week before, erased the memories of a dreadful 41-17 loss at Arizona and won its 200th home game in franchise history.
The Chargers (3-4) failed to build off the momentum of a 30-10 win over New England last week, and faced a long flight to London for next week's game against New Orleans at Wembley Stadium.
Rivers went 22-of-29 for 208 yards and two touchdowns, but had a sloppy outing for a quarterback that entered the game with the NFL's top passer rating. He committed three turnovers, including two fumbles.
Malcom Floyd had four catches for 65 yards, including a 14-yard touchdown, while Vincent Jackson also scored with a 12-yard catch. The Chargers were minus No. 1 receiver Chris Chambers, who missed his second straight game with a sprained left ankle.
The electricity initially went out about a half-hour before the game after three small helium balloons became entangled in power lines across the street from the stadium.
Power was restored about 10 minutes before the 1 p.m. start time. It lasted for about 10 minutes, and went out early in the first quarter shortly after the Chargers' opening possession. Play resumed after a 15-minute break, and continued while the power was out for about 45 minutes. The power went out once again at the 2-minute warning and wasn't fully restored in the stadium until midway through the third quarter.
CBS was unable to broadcast the game while the power was out, leaving fans on two ends of the country watching other games.
For those who missed it, it was a back-and-forth game in which the teams traded the lead four times, with Buffalo going ahead for good when Lynch scored to cap a nine-play, 78-yard drive. Edwards kept the drive alive with a 12-yard scamper on third-and-7, and set up the score with a 22-yard pass to Roscoe Parrish.
Lynch then rumbled around the right corner, and reached the end zone courtesy of a big block from fellow running back Fred Jackson.
With no power, though, the atmosphere was a little surreal. The crowd would cheer without prompting and there was none of the loud music being pumped in through the expensive sound system. Also missing were the commercials being broadcast during breaks in the action.
On-field officials kept time, while the back judge took care of the play clock, putting up his hands to indicate 10 seconds remaining. That led to NFL officiating observer Art McNally to yell out in the press box, "That's how we used to do it!"
It was a throwback type of game between two original American Football League franchises, who met twice in the AFL championship game. The Bills won both times in 1964 and '65.
The Atlanta Falcons have agreed to a five-year contract extension with wide receiver Julio Jones. Sources say he will receive $71.25 million total, with $47.5 million guaranteed.
Randall Cobb, who fell hard on his right shoulder on the third play in Saturday's 39-26 preseason loss to the Eagles, avoided major injury but will have additional tests done Sunday.
Redskins coach Jay Gruden said he was left like everyone else -- scratching his head over how Robert Griffin III went from being cleared one day to out the next with concussion symptoms.
Dallas Cowboys wide receiver Dez Bryant will go into the regular season without having taken a snap in the preseason.
Bengals QB Andy Dalton left Saturday's 21-10 preseason win over the Bears as a precaution with a neck injury that appeared to happen on his first and only series of the night.
Baltimore Ravens wide receiver Steve Smith and Washington Redskins cornerback Chris Culliver were ejected with less than a minute left in the first quarter of Saturday night's preseason game.