Jerod Mayo made his first mistake before the New England Patriots even took a snap against the Los Angeles Chargers on Saturday.

About 30 minutes before kickoff at Gillette Stadium, Mayo told 98.5 The Sports Hub’s pregame radio show that Antonio Gibson would start at running back over Rhamondre Stevenson. The announcement wasn’t necessarily surprising, as Mayo suggested earlier in the week that Stevenson could be benched after he lost his seventh fumble of the season against the Buffalo Bills last Sunday.

When the game began, however, it was Stevenson in the backfield for New England’s first offensive drive, and Gibson watching from the sideline as Stevenson picked up a 5-yard gain on the Patriots’ first play from scrimmage.

The about-face baffled NFL Network color analyst Ross Tucker, who suggested that Mayo had also told the broadcast crew that Gibson would start instead of Stevenson. So, why the sudden about-face?

Mayo didn’t provide many answers after the game.

“That was just a coach’s decision,” the Patriots head coach told reporters in his postgame press conference. “Coach’s decision.”

When asked what led to Stevenson starting over Gibson — and whether anything transpired in the 30 minutes before kickoff that may have led to the change — Mayo again was tight-lipped.

“I understand the question,” Mayo responded. “Look, it’s a coach’s decision. That’s all I’ve got on that.”

That’s a wholly unsatisfying explanation for an odd controversy that was entirely of Mayo’s making. If the first-year head coach simply had said he’d decide at kickoff who would start at running back — or just not announced that Gibson would start — we wouldn’t be having this conversation. By saying one thing and doing another, however, Mayo makes himself and his coaching staff look dysfunctional.

And by declining to provide specifics after the game, he opens the door on all kinds of speculation about why Stevenson started instead of Gibson — an otherwise minor development that had no bearing on the Patriots’ lopsided 40-7 loss.

“It’s just an unforced error,” Patriots Insider Tom E. Curran said of Mayo’s decision on Patriots Postgame Live. “If you’re not going to start (Stevenson), or if you are going to start him, the game doesn’t hinge on that conversation. Everybody understands the guy is going to play football on this day. He’s one of your better players. So, when someone says, ‘Who’s starting?’ Say, ‘I haven’t decided yet. We’ll decide when we get out there.’

“You don’t have to make it a one-car accident, which is what he did by giving an answer that he can’t stick to.”

Stevenson finished with one rushing yard on two carries — his only other carry after his 5-yard gain was a 4-yard loss — while Gibson tallied 63 yards on 12 attempts.