QB Nick Mullens to start again.

The feel-good story of Nick Mullens will continue playing in prime time.

On Tuesday, the 49ers’ recently anonymous third-string quarterback said head coach Kyle Shanahan told him he would remain the starter when the 49ers host the Giants on Monday night.

Mullens, 23, earned a second career start based on his impressive debut before a national audience in a 34-3 romp over the Raiders on Thursday night. He completed 16 of 22 passes for 262 yards with three touchdowns and no interceptions. His passer rating (151.9) was the highest by a 49ers quarterback since Alex Smith (157.1) on Oct. 29, 2012.

“It was a great experience, but it’s obviously on to the next week,” Mullens said. “As this league is, one week doesn’t make a season, so we have to keep things rolling.”

Mullens, an undrafted free agent from Southern Mississippi in 2017 whom Shanahan jokingly termed the 49ers’ “secret weapon” last week, won’t be a surprise to the Giants. Running back Matt Breida smiled when asked how New York might prepare for him differently than the Raiders.

“I think they’re going to be like, ‘Oh, crap, this guy’s good,’ ” Breida said. “And they’re going to put a few more people back there to cover just because of the throws that he made.”

Mullens has assumed the spot of C.J. Beathard, who backed him up against Oakland because he was dealing with a sprained right wrist. Last year, as a rookie, Beathard was replaced by Jimmy Garoppolo after he went 1-4 in his starts. This season, he went 0-5 after Garoppolo was sidelined with a torn ACL.

“It’s tough … two years in a row kind of going through it,” Beathard said. “It’s something that’s going to make me stronger in the end, I feel like. I think God’s testing me. I think it will make me a better person and a better quarterback in the long run.”

For his part, Mullens isn’t looking too far ahead. And he’s finished thinking about a debut that had him choking back tears in a postgame interview with Fox’s Erin Andrews.

“I’m done reflecting on it, to be honest,” Mullens said. “It’s time to get to the Giants. But it was a very cool moment. I try to give it everything I have. And when your work pays off, it’s exciting.”