Sean Mannion will open the season as Rams’ backup QB, and he’s ready if needed

Sean Mannion might one day be known as the quarterback who forced Jared Goff to the inactive list.

For one game at least.

Mannion, a second-year pro, enters Monday night’s season opener at San Francisco as the Rams’ No. 2 quarterback behind starter Case Keenum.

Goff, the No. 1 pick in the NFL draft, will be on the sideline wearing a Rams sweat suit.

Mannion had an inkling he would be the backup after last week’s exhibition loss at Minnesota, when Coach Jeff Fisher said Goff was “not ready” and that Mannion would probably be No. 2 against the 49ers.

On Monday, Mannion said quarterbacks coach Chris Weinke reiterated that scenario. Fisher made it official Tuesday.

Players were off Wednesday, but Mannion will be taking second-team reps when the Rams begin game-week preparations Thursday at Cal Lutheran.

“It feels good for the coaches to put me in that position,” Mannion, 24, said this week. “Going back to April [off-season workouts], I’ve been happy with the way I’ve been playing and the throwing the ball.

“To have your effort rewarded and to be put into this position is great, and something I take very seriously.”

Monday night’s game will be a homecoming of sorts for Mannion, who played at Pleasanton Foothill High, located about 25 miles from Levi’s Stadium in Santa Clara.

Mannion went on to Oregon State, where he became the Pac-12 Conference’s all-time passing yardage leader.

The Rams selected the 6-foot-6, 233-pound Mannion in the third round of the 2015 draft and he opened the season as the No. 3 quarterback behind Nick Foles and Keenum.

Mannion was inactive for the first 10 games. However, with Keenum sidelined because of a concussion suffered against the Baltimore Ravens, Mannion relieved a struggling Foles against the Cincinnati Bengals and completed six of seven passes for 31 yards.

The Rams’ trade to the top of last April’s draft to select Goff eventually led to Foles’ release. Mannion was regarded as the No. 3 quarterback behind the competition between Keenum and Goff for the starting job.

That competition never materialized because of Keenum’s sold play and Goff’s inconsistency and mistakes.

Meanwhile, Mannion impressed during training camp — “You can see the throws, you can see the poise, you can see the decision-making,” Fisher said a few weeks into workouts — and performed fairly well in three exhibitions.

After Goff played only two series in the exhibition opener against the Dallas Cowboys, Mannion came on and passed for three second-half touchdowns in a come-from-behind victory. Mannion did not play against the Kansas City Chiefs, but he entered the game late in the third quarter at Denver and played the second half at Minnesota.

He completed 39 of 60 passes for 325 yards and four touchdowns, with one interception.

“For the most part, I thought I played efficient football, put together some good drives and executed the offense,” Mannion said. “There are some things to work on, but for the most part I was accurate.”

Now Mannion is again one play away from going into the game.

Fisher indicated that he would probably switch Mannion and Goff for Week 2. That probably won’t change Mannion’s approach. From the time he joined the Rams in rookie camp last year, he has prepared each week as if he would start, he said,.

He will be ready, if needed, on Monday night.

“I feel way more comfortable,” he said. “You’re learning initially, but then once you learn it and have a year to work on the repetition of actually doing it on the field, it compounds that effect it has on your comfortability.”

Bonus baby

Offensive tackle Rob Havenstein was happy to move into the starting lineup last season as a rookie.

Everything else was a bonus, including the nearly $190,000 he received through the NFL’s performance-based pay program. The bonuses were announced in March.

“I saw it on Twitter or something like that,” Havenstein said this week. “I thought it was cool, obviously, but a bonus is just a bonus.

“It’s not something I was playing for. I just wanted to go out and do the best I could. And I’ll do the same thing this year.”

The yearly program was implemented as part of the NFL’s 2002 collective bargaining agreement with the NFL Players Assn. The formula for bonuses weighs playing time against salary.

Each team had a distribution pool of about $3.8 million, which does not count against the salary cap. Havenstein, a second-round draft pick from Wisconsin, had a base salary of $435,000, according to spotrac.com. He started 13 games.

His preparation for this season was stalled because of a foot injury.

The 6-foot-8, 321-pound Havenstein was sidelined for organized-team activities and nearly all of training camp, but returned to start the final exhibition against Minnesota.

He is listed behind Rodger Saffold on the Rams’ depth chart, and said he still was honing his pass-protection sets for the opener.

“That’s something I’ll be working on extra after practice,” he said. “Something I can’t get enough of are reps.”