As he was ticking off the reasons for optimism on his new team Tuesday, outside linebacker Elvis Dumervil, 33, mentioned a 22-year-old cornerback.

“I’m excited about Rashard Robinson,” Dumervil said.

Oh, really? What excites you about him?

“I think,” Dumervil said, “he can be the best corner in this division.”

The best in the NFC West? The home to perennial All-Pros in Arizona’s Patrick Peterson and Seattle’s Richard Sherman? Dumervil, who spent his first 11 seasons in the AFC, was reminded about the players in his new division.

“That’s what I’m telling you,” Dumervil said, not backing off his belief in Robinson. “I know who the corners are.”

Dumervil, a five-time Pro Bowl selection, knows about competing at a high level. And he thinks Robinson has the “right mind-set” and competitive spirit to prove him prophetic.

Those qualities were on display Friday when Robinson began the preseason opener in Kansas City by resembling one of the worst cornerbacks in the NFC West.

After enduring a humiliating opening drive, however, the 2016 fourth-round pick was unfazed: The defensive back known for his trash-talking swagger kept his motor mouth moving.

“I took that drive and I sat down on the sideline and told my teammates ‘I’m going to make up for it. I got y’all.’ And that’s what I did. … You just have to keep your composure.”

In the first six minutes, Robinson allowed completions of 32 and 29 yards and badly whiffed on a third-down tackle that would have prevented a first down on Kansas City’s game-opening touchdown drive. However, he bounced back on the Chiefs’ second drive to tackle running back Spencer Ware for no gain and return an interception 30 yards two plays later.

“Every single corner is going to get beat, but not every corner can respond the way he did,” defensive coordinator Robert Saleh said. “For a young guy, 22 years old, to have all that happen to him and to show the resolve, the fight, and the dog that we’ve talked about with him … for me, that stamped everything that Rashard’s going to be for us. He’s going to be a very good corner.”

Considering the 49ers’ cornerback cupboard, Robinson better be.

After he had one interception in a solid six-start rookie season, Robinson headlines an inexperienced unit. The candidates to start opposite him are Dontae Johnson (six career starts) and Keith Reaser (0), meaning the 49ers’ top three cornerbacks have combined for three career interceptions.

In the offseason, the 49ers released starting cornerback Tramaine Brock after he was arrested on felony domestic-violence allegations (charges were later dismissed). They addressed the need by drafting cornerback Ahkello Witherspoon, but the third-round pick has spent training camp with the second-team defense.

That means Robinson will be the corner to shadow the NFL’s top wideouts. This season, the 49ers will face four players (Indianapolis’ T.Y. Hilton, Seattle’s Doug Baldwin, Arizona’s Larry Fitzgerald and the Giants’ Odell Beckham Jr.) who had at least 90 receptions in 2016.

Robinson figures to get beat, but he’s focused on not getting upset.

“A play goes wrong, you can’t just lose it,” Robinson said. “You’ve got to stay to stay composed and just go out there and play ball. They get paid just like we get paid.”

And, if Dumervil is accurate, Robinson one day will be compensated with a hefty second contract.

“I think he just has the mind-set,” Dumervil said. “He likes to compete. He likes to have fun. He’s a dog — a dog is a guy who no matter what, he’s going to bring it. I’m excited to really see him shock some people in this division.”

Eric Branch is a San Francisco Chronicle staff writer. Email: Twitter: @Eric_Branch

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