ORCHARD PARK, N.Y. — It’s hard to understand what Buffalo Bills coach Doug Marrone and defensive coordinator Jim Schwartz saw in the first two weeks that convinced them to start Leodis McKelvin at cornerback against San Diego opposite Stephon Gilmore, rather than Corey Graham.

Graham was the Bills’ best defender heading into the San Diego game, but there he was, standing on the sideline when the Bills defense took the field for its opening series, which ended in a San Diego touchdown. Meanwhile, McKelvin had given up 10 pass completions in the opener against Chicago, then played OK in the win over Miami, even intercepting a pass on the final series of the game. Still, that didn’t warrant the start over Graham, who had broken up a league-high six passes and made 13 tackles in the first two games.

“We just rotate the guys in; I don’t think there’s really anything to look into it,” Marrone said.

Gilmore played 49 of 66 defensive snaps, McKelvin played 46, and Graham 33, though some of those come at safety due to injuries to Aaron Williams and Da’Norris Searcy. Chargers quarterback Philip Rivers completed 18 of 25 passes for 256 yards and two touchdowns, didn’t have a ball intercepted and only one of his seven incompletions was the result of a breakup, that by Graham.

Gilmore gave up five completions on five targets for 59 yards and a touchdown, a play where Rivers threw a quick screen to Eddie Royal who used a nice block to scoot past Gilmore into the end zone. Graham was targeted twice, broke up one pass and allowed a four-yard completion. McKelvin was targeted twice and gave up two catches for 55 yards including a 49-yard one-on-one sizzling by Malcom Floyd.

“We all want to start,” Graham said. “You name a cornerback or a player that don’t want to start, you’re probably naming a guy that don’t got a job. We’re all competitive. We want to start. We want to play as much as possible. This is just how it is. We’re going to have a rotation. That’s going to happen regardless. But I’d be sitting here, lying if I said I didn’t want to start.”

Marrone has said routinely that the Bills believe all three are starter worthy, and that by rotating them, they save wear and tear on each player. That’s fine in theory, but it’s clear that Gilmore and Graham should be getting the bulk of the snaps.

“It is hard,” Gilmore said of rotating in and out. “I want to be on the field every snap to help my team win, but that’s coach’s call. That’s what it is. I wouldn’t say it breaks my flow, but once I’m locked in I’m locked in and when I come out, you’ve got to really stay locked into the game.”

Gilmore sat out the opener with a groin injury, and there was no way Marrone could not start Graham against Miami after the way he played in Chicago, almost single-handedly saving the game with two late pass breakups in the red zone, plus an earlier interception and 45-yard return that set up a touchdown. However, McKelvin – who has been a starter on and off in Buffalo since being a first-round pick in 2008 – got the call against Rivers and the Chargers.

To be fair, the secondary as a whole had a rough day, not only with some blown coverages and assignments, but with missed tackles and penalties (four on the DBs for 57 yards). “I think it was communication, we weren’t all on the same page,” said Gilmore. “We know our rules, but if one person’s not on the same page, that’s when somebody leaks, especially on the back end.”

Also, it didn’t help that strong safety Searcy left midway through with an ankle injury, and nickel corner Nickell Robey had another rough outing and was benched in the second half in favor of Ron Brooks.

“They got us over the top twice,” Marrone said of the 49-yard go-routes Floyd caught over McKelvin and Robey. “It’s one of those things. You’re playing against a good group of skill guys and a veteran quarterback, so you’ve just got to keep fighting and battling. Those guys are going to make plays. Unfortunately, they made them against us (Sunday). We’ve got some guys that are banged up out there, but at the same time, it’s hard. We had them a couple times throwing off rhythm and we weren’t able to make a play.”

REPORT CARD VS. CHARGERS

PASSING OFFENSE: C-minus – Nearly a third of EJ Manuel’s 238 passing yards came on the final garbage time possession when the Chargers were sitting back and giving him anything he wanted underneath. Manuel didn’t get much help from his offensive line, which had a tough time controlling San Diego’s pass rush and sacked him three times for 33 yards in losses. WR Sammy Watkins had only two catches for 19 yards on eight targets, and there were several throws where Manuel and the intended receiver weren’t in sync. A frustrating day all around.

RUSHING OFFENSE: D – With the wind blowing hard, offensive coordinator Nathaniel Hackett tried to establish a ground game, but his insistence on running up the middle, particularly with C.J. Spiller, was ill-fated. The offensive line was getting pushed back all day, and there was nothing there, but Hackett kept trying to pound it in there. Spiller had just 25 of the 87 rushing yards, and he was stopped on a key 3rd-and-1 in the fourth quarter when the Bills were near midfield and trailing by 10.

PASS DEFENSE: D – The secondary had a rough day. There were blown coverages, missed tacklesand penalties, all of which helped the Chargers to extend drives. They had a 17-play field goal drive, and 14-play touchdown drive. The pass rush produced just one sack and that was by backup LB Manny Lawson. Nickell Robey and Leodis McKelvin were both burned for 49-yard bombs by Malcolm Floyd, and TE Ladarius Green made a nice living on crossing routes through the secondary.

RUSH DEFENSE: B – The Chargers ran it 37 times and gained only 85 yards, a paltry 2.3 yards per attempt, so by that standard, it wasn’t a bad day for Buffalo. The Chargers made only four of their 20 first downs via the rush. Of course, they were using their third-string back, Donald Brown, almost the entire game, but that didn’t prevent the Chargers handing him the ball 31 times. What the run game did was run the clock and keep the Bills off balance, opening up the passing game.

SPECIAL TEAMS: B-plus – This was a wash as neither side had an advantage in the kicking game. Despite a fierce wind, Colton Schmidt averaged 44.0 net on five punts, and Dan Carpenter made a 45-yard field goal. The punt coverage unit allowed six yards on three returns, but despite solid overall play, it didn’t translate into any field position advantage or big plays like last week against Miami.

COACHING: D – The Bills had a chance to go 3-0 with a win over a good team playing in their stadium. But neither side of the ball played well and the result was a sloppy loss. Hackett couldn’t get the offensive line together, and he never developed a rhythm, though there were some plays to be made that weren’t. On defense, coordinator Jim Schwartz had a tough time because his defensive backs couldn’t stop getting beat, committing penalties or getting hurt. There were too many long possessions for the Chargers.