SANTA CLARA, Calif. -- In the middle of a lost season, the San Francisco 49ers have found some promising young players.

Maybe none has been more surprising than quarterback Nick Mullens.

"Nick Mullens has stepped up to the moment week in and week out and he's showing he can play in this league," cornerback Richard Sherman said. "I just hope we can keep him because teams need a quarterback. This guy is not just playing like, 'Oh, conservative football, get the ball in the right places.' He's making the right decisions. He's making good throws under pressure.

" ... You've got guys that are out there right now that are not playing better football than Nick Mullens and he could be a starter for a lot of teams in this football league."

Sherman isn't exactly the type to hand out praise unless it's warranted, particularly to quarterbacks, but given Mullens' ascent from undrafted rookie to practice squad to backup to C.J. Beathard to starter to leading the charge for San Francisco's first win against Seattle in 11 tries, it's hard to find falsehoods in anything he said.

Against Seattle, Mullens was 20-of-29 for 275 yards with a touchdown for a passer rating of 110.6. In two games in three weeks against the Seahawks, Mullens threw for 689 yards, the most passing yards by any quarterback in a season against Seattle since it entered the league in 1976.

Since becoming the starter in Week 9, Mullens ranks sixth in the league in passing yards per game (292.3,), third in yards per attempt (8.64), 15th in passer rating (96.0) and 16th in total QBR (57.9). Although some of those stats can be attributed to weaker opponents like the Raiders and the second half of a blowout loss, Mullens has proven he can play and deserves a spot on a quarterback depth chart moving forward.

What's more pressing, at least from a Niners perspective, is figuring out what his value is to them, what it might be to other teams in the league and how best to move forward with him beyond 2018.

Are they best served to hold on to Mullens as the No. 2 behind Jimmy Garoppolo, especially with Garoppolo coming back from ACL surgery? What if a team offers a pick within the first three rounds? Those are things the 49ers and coach Kyle Shanahan will have to consider.

"I mean, you're open to anything possible that improves your team," Shanahan said. "That's not just backups. ... I think backups are extremely valuable, not just at the quarterback position, but everywhere. Usually you have to win with backups and you hope to stay healthy all of the time, but very rarely does that happen. Backups can be the difference in a season."

For all intents and purposes, Mullens has made the case he can be an ideal backup to Garoppolo. He has won half of his six starts in Garoppolo's stead and comes with the added bonus of being cost-effective, which helps offset the exorbitant amount the Niners are paying Garoppolo.

As an undrafted free agent, Mullens' contract will expire after the 2019 season, at which point he would become an exclusive rights free agent and the Niners can retain him at the minimum price associated with that. From there, the Niners would still retain control after the 2020 season as a restricted free agent.

The price, for the 49ers, is more than favorable over the next few years and the team is pleased with how he has come along. So much so that, barring injury, Mullens will get to finish this season as the starter rather than a return to Beathard.

"Nick deserves to be in," Shanahan said. "Nick's played very well and he's gotten better as he's gone. I thought [the Seattle game] was probably Nick's best game, especially the way he finished it in that fourth quarter. ... He's done too good of a job. We'd love to get C.J. more playing time, but Nick's earned it and I'm not taking him out."

To this point, Shanahan has preferred not to make sweeping declarations about whether Mullens or Beathard, a 2017 third-round pick, will be the No. 2 quarterback in 2019. A few weeks ago, he said the two quarterbacks would be "dead even" going into the offseason. There's also no reason to make that call now.

There are also recent examples of Shanahan and the Niners going with the player who performs better than the one who was more highly drafted. San Francisco rolled with undrafted running back Matt Breida over fourth-round pick Joe Williams in 2017 and then released Williams this year when others outperformed him.

Shanahan has said Beathard had the upper hand after Garoppolo went down based on what took place in practice each day. When Mullens got the opportunity because of Beathard's injury, he made the most of it, which is why Shanahan has continued to play him.

Now Mullens has to build on what he has done so far. Barring a crazy trade offer, the Niners would be wise to hang on to him until they see Garoppolo make a complete recovery and produce in 2019.

As Sherman bounded off the stage following last week's win, he stopped and told Mullens that he had nothing positive to say about him. A sheepish Mullens laughed and offered a simple thanks as he stepped to the podium with the swagger of a quarterback unafraid to meet the plaudits Sherman had just lavished on him.

"You can't play if you're not confident," Mullens said. "So, I always take the field as a confident player. I'm confident in my teammates, as well. ... Confidence: the more you play, the more you do it, the better you feel."