Which rookies stood out in 49ers preseason opener? Kyle Shanahan provides answers

Watkins had three total catches for 56 yards, but he also had a rough moment when cornerback Ja'Quan McMillan stepped in front of him for an interception. The big catch and the interception added up to a mixed performance for Watkins, as Shanahan pointed out in his postgame analysis.

"I thought he did some good things, especially that 50-yard catch," Shanahan told reporters Saturday evening. "But he also had some plays where he struggled too. Getting that pick, you know, he busted the route on that, which that was a big one. So making that big play on the first third down of the game and our third play is what allowed us to get that opening drive with the score. But kind of a typical rookie game. There's some positive in it, but a lot of stuff that we can challenge him with when we watch the tape with him Monday."

Quarterback Mac Jones, who threw both the 50-yard catch and the interception, told reporters he's still in the process of creating chemistry with Watkins but that the rookie had a solid overall performance.

"I'll have to watch it, but I know what I saw on the field was just like the safety kind of went to the right, so I had the one-on-one and me and him -- he's a rookie, right? So we're working on our timing and everything," Jones said. "And I thought he played well overall and made a great play on that down the field throw early in the game to kind of set the tempo of the game. But he's doing a good job in practice. I feel like we're connecting a lot in practice and we'll just continue to grow. It was his first NFL game and I thought he did a good job."

Like Watkins, Martin will have his share of pluses and minuses to take from Saturday's game. Martin finished with five tackles but also had missed tackles to learn from.

"He ran around, got a lot of playing time," Shanahan said. "He had a couple misses, especially on a big third down on a shallow cross across the field, just got his eyes a little too nosy with the back. I like how Nick's been going, but I think there's a lot of tape that he can get better from watching this today."

Also making an early impression was seventh-round pick Junior Bergen, who has a chance to ride his prowess as a return specialist to a roster spot. Bergen showed that ability with a 28-yard punt return in the first half.

Bergen also had two kick returns for 40 yards and was targeted once in the passing game.

"He made a good cut," Shanahan said of Bergen's punt return. "There was a guy down there and he made that guy miss and broke their contain. Thought it was a hell of a play. Those are his opportunities. Wish he got more in the game, but no, that was a hell of a play by him."

Sigle drew some of the strongest praise from Shanahan out of the rookie players. Sigle finished with seven tackles, which Shanahan said was a fitting finish to what has been a strong week.

"I thought he was one of the guys who flashed a lot tonight," Shanahan said. "He got a little bit of late start, being injured in the offseason and I think it was a few days into camp where he really got going. But he's had a hell of a week here and finished it off good today."

But while Shanahan had plenty to say about his draft picks, some of his strongest praise came for an undrafted player. That would be defensive tackle Sebastian Valdez, who finished with four tackles, one quarterback hit, and half a sack.

"I'd say he flashed the most today, just noticing him out there," Shanahan said.

Usually at least one undrafted rookie jumps out during training camp and the preseason and plays well enough to snag a spot on the 53-man opening day roster, and it sounds like Valdez has a shot at being this year's version.

"I mean, he's been flashing a lot in practice," Shanahan said. "He's been a problem in one-on-ones and it looked like he played the run real well today. When our line coach talks about him in practice, that means he's doing some stuff, and it was good to see him carry over to the game today."

The 49ers will be back in action next Saturday in Las Vegas against the Raiders (4 p.m. ET/1 p.m. PT). It'll be another important game for the aforementioned players to make their case, but for those like Watkins, Sigle, Bergen, and Valdez, who need to make their chances count in order to ensure a spot on the roster and/or depth chart, it sounds like they already have plenty to build on from their preseason debut.