Wilmer Difo has made an Opening Day roster for the first time. (Toni L. Sandys/The Washington Post)

ANNAPOLIS — Saturday afternoon’s exhibition against the Red Sox at the U.S. Naval Academy’s Max Bishop Stadium was the Nationals’ final tuneup before Monday’s season opener. Therefore, it was, theoretically, a chance for a couple Nationals players to make a final case for a sport on the Opening Day roster.

But the decisions were already made by the time Max Scherzer threw the game’s first pitch. Wilmer Difo and Michael A. Taylor, both of whom spent spring training competing for a roster spot, were informed Friday they will break camp on the Opening Day roster, according to people with knowledge of the situation. On the opposite end, Jeremy Guthrie, the final nonroster invitee and long-reliever option in camp, was not with the club Saturday, though Manager Dusty Baker declined to confirm whether he had been cut.

“We don’t have to announce it for a couple days,” Baker said.

The decision to go with Difo and Taylor signals that either right-hander Joe Ross will start the season in the minors or a position player will start on the disabled list. Baker, however, said there aren’t any injury concerns beyond Anthony Rendon’s bruised calf, which is not considered serious. Rendon’s status for Opening Day remains unclear, but he took batting practice for the first time Saturday since fouling a ball off his calf earlier this week. He said he didn’t want to push it for an exhibition and expects to play Monday against the Marlins. Baker didn’t sound as confident.

“He’s doing better,” Baker said. “He’s still a little sore. He’s not playing today, and he might even be at question a little bit for Opening Day. We’re not sure, but we’d rather have him miss Opening Day possibly because we got a day off after that and be ready to play the next day than take a chance and miss him for 10 days or two weeks.”

Sending Ross to the minors is a strong possibility because the Nationals don’t need a fifth starter until mid-April thanks to the number of off-days early on. Washington could then carry the standard seven-man bullpen with an unusual six-man bench. The Nationals would avoid using one of Ross’s option years if he is promoted to the majors within 20 days.

The 26-year-old Taylor provides the Nationals a natural backup center field. Difo, who turns 25 Sunday, is a shortstop by trade — and perhaps the Nationals’ best defensive shortstop — but the switch-hitter has also spent ample time at second base, played third base for the first time last season and debuted in center field this spring. It is the first time Difo, who signed as an 18-year-old out of the Dominican Republic in 2010, will make the Nationals’ Opening Day roster. Chris Heisey, Stephen Drew, Jose Lobaton and Adam Lind compose the rest of Washington’s projected bench.