It says something to what expectations for the Raiders cornerbacks were when they rank last in the NFL in pass defense through six games — and the thinking is that it could be worse.

But Oakland has unquestionably made strides. In their past two games, the Raiders held Peyton Manning without a touchdown pass and then shut down Philip Rivers. Rivers didn’t have any touchdown passes through three quarters, but finished with three after the Raiders called the dogs off with a 37-6 lead.

In the words of cornerback DJ Hayden, “The sky is the limit with us.”

The cornerbacks group has even held up with the move of TJ Carrie, the No. 1 corner throughout training camp and the preseason, to safety to fill in for injured Nate Allen.

Hayden, David Amerson and Neiko Thorpe have persevered.

“We’re extremely talented, we’re just young,” defensive backs coach Marcus Robertson said. “It was going to take time for those guys to grow. We changed some of the technique. We’ve been working it for quite some time, and you can see they’re getting better.”

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Robertson said he’s changed the players’ stances and what they’re looking for and when.

“The little things that hopefully make a big difference come game time,” Robertson said

Robertson is one of few holdovers from last year’s staff — at the strong urging of future Hall of Fame safety Charles Woodson — and has fit in well with head coach Jack Del Rio and the new staff.

“We’re changing the mentality of the entire defense,” Robertson said. “Guys are playing with a lot of confidence and trusting in one another.”

Look no further than Hayden, the team’s No. 1 pick in 2013, who has battled injuries and ineffectiveness.

General manager Reggie McKenzie said this week that he always had faith in Hayden, who is coming off a game in which he had an interception, a forced fumble and 10 tackles.

“He had a couple of injuries that just kept nagging him,” McKenzie said. “Once he got over that, I feel like his body was stronger enough to be more physical in his play. And with that he began to get confident.

“That was his No. 1 thing. He just wasn’t a confident player, for whatever reason. I think he feels good about his athletic ability and his body now. He’s got a ways to go that way, but as soon as he realizes his skill set he’s going to be a solid football player.”

“Solid” may not be what fans want to hear about a No. 12 overall pick, but Hayden has filled out his 5-foot-11 frame and is starting to turn his head around faster and make plays on the ball.

“He’s doing a much better job with technique. When he finally realizes his potential,” Robertson said, “we’re going to have an outstanding player.”

Hayden rolls his eyes a little at talk of not being confident, and talks about his improvement as a whole, along with the other corners.

“We just have to keep progressing, and everything else will take care of itself,” Hayden said.

It helped that Washington waived Amerson on Sept. 21. Oakland claimed him the next day, and the 6-foot-1, 205-pound Amerson has been a fixture in the starting lineup the past three games.

“I studied him when he came out of college (three years ago) and he has all the tools to be an outstanding player,” Robertson said. “When he became available, we were just elated to get a guy of that caliber. We are talking about a guy that was drafted in the second round.”

Teams don’t normally have a chance to add a second-round talent the third week of the regular season.

“You give him a clean slate,” Robertson said. “Give me the talent and I will coach the talent. I get them to fall in line with what we’re preaching here and they will be successful.

“They already have the ability.”

Vic Tafur is a San Francisco Chronicle staff writer. E-mail: vtafur@sfchronicle.com Twitter: @VicTafur