Jared Goff struggles in Rams’ final preseason game, a 27-25 loss to the Vikings

He began the exhibition season with designs on possibly starting the season opener.

Several rookie quarterbacks selected as the No. 1 pick in the NFL draft achieved that feat.

Jared Goff won’t be the Rams’ starter. He probably won’t be the first quarterback off the bench if starter Case Keenum is injured in the season opener against the San Francisco 49ers.

Not after Goff struggled again in the Rams’ final exhibition, a 27-25 defeat to the Minnesota Vikings on Thursday night at U.S. Bank Stadium.

“He’s not ready,” Coach Jeff Fisher said, “but he’s really, really made significant progress.”

The Rams open the season on Sept. 12 on “Monday Night Football.”

Asked if he had enough confidence in Goff to make him the backup if something were to befall Keenum, Fisher said second-year pro Sean Mannion would be the first option.

“I think it’s going to take a little bit more time,” he said of Goff. “That isn’t to say he can’t be a [No. 2 quarterback] when we start. But if you were starting right now, I’d probably have Sean as the 2.”

On Thursday, with Keenum and other frontline players out of harm’s way on the sideline, Goff started for the first time. He looked sharp on his first series, moving out of the pocket for two impressive completions and finishing it with a one-yard touchdown pass to receiver Kenny Britt.

But he thereafter struggled with accuracy and confidence — several dropped passes did not help — and he committed turnovers on two consecutive plays near the end of the first half.

He was anything but sparkling in a new stadium that was designed by the same firm in charge of the Rams’ new Inglewood home that will open in three years.

Still, Goff said he remained confident with how he has progressed.

“I’ve come a long way,” he said. “I feel good where I’m at.”

The nadir for Goff and the Rams came with less than two minutes remaining in the first half.

Goff dropped a perfectly good snap in the shotgun formation and lost a fumble at the eight-yard line that led to a field goal.

On the first play of the next series, Vikings end Justin Trattou tipped a pass into the air, and tackle Toby Johnson grabbed the ball for an interception. The Vikings scored on the next play.

Goff played the first half and completed six of 16 passes for 67 yards and a touchdown, with an interception and fumble. In four exhibitions, he was 22 of 49 for 232 yards and two touchdowns, with two interceptions and three fumbles.

“It’s all about being patient with him,” Fisher said. “He’s not frustrated or anything. He’s encouraged.”

The Rams concluded the exhibition season with a 2-2 record, defeating the Dallas Cowboys and Kansas City Chiefs at the Coliseum and losing on the road to the Denver Broncos and Vikings.

On a night when the field was populated mainly with reserves, Fisher tried to keep Goff safe in his last extended opportunity.

Veteran Rodger Saffold was at left tackle in place of injured Greg Robinson and Rob Havenstein returned from a foot injury to start at right tackle. Britt provided an experienced target.

Linebacker Akeem Ayers and safety Maurice Alexander were the only regular defensive starters for the Rams, who were facing a Vikings team, and fan base, still in shock about quarterback Teddy Bridgewater’s season-ending knee injury.

Rookie Joel Stave, who led Wisconsin to a Holiday Bowl victory over USC last season, started for the Vikings in place of Bridgewater.

With rosters needing to be trimmed from 75 to 53 players by Saturday, at least one Ram came through with a big performance in final auditions.

Defensive lineman Morgan Fox, an undrafted free agent from Colorado State Pueblo, had two sacks and several impressive stops.

“I was trying not to think about that too much,” Fox said of the impending cuts. “It makes you play a little slower.”

Others did not aid their causes.

Veteran receiver Brian Quick struggled again with drops. And players trying to make the roster or practice squad with special teams play did not help themselves by missing tackles on Jhurell Pressley’s 106-yard kickoff return for a touchdown.

Paul McRoberts caught a touchdown pass from Mannion, but he also muffed a punt that led to a touchdown.

And then there was Goff.

The Rams trailed at halftime, 13-7, after Goff’s turnovers allowed the Vikings to score 10 unanswered points.

Goff started well, completing a 22-yard pass to running back Chase Reynolds and a 30-yard pass to Bradley Marquez that helped set up his touchdown pass to Britt.

But the next six series ended with punts or turnovers.

He said he would use the experience he gained in four exhibitions to improve.

“The good things I did and all of the stuff I can learn from,” he said. “Obviously, there’s a lot of both.”

gary.klein@latimes.com