The rule that prohibits rookies from joining NFL offseason programs until classes at their colleges have ended, really, has little impact on the top draft picks.

The young players who face the biggest challenges are those who must make an immediate impression in order to win a job.

“Christian McCaffrey and Solomon Thomas, those guys get all the attention because they’re first-round picks,” 49ers coach Kyle Shanahan said. “But those are the guys who are going to be all right, regardless of whether they miss an offseason.

“It’s more of the guys like Kendrick Bourne, who was undrafted and other people like that, who are battling to make roster spots who have only been here for a few weeks, it really puts them behind the eight ball.

Bourne was allowed to take part in only the final day of organized team activities due to the late ending of classes at Eastern Washington. The pass-catcher has been playing catch-up since reporting to training camp in Santa Clara.

“I was definitely kind of struggling, definitely messed up a couple of routes during camp,” Bourne said. “(Receivers coach) Mike (LaFleur) was kind of not trusting me. I was struggling with some of the stuff I couldn’t remember and I was busting routes.”

But in the 49ers’ first exhibition game Friday against the Kansas City Chiefs, Bourne made his identity known with four receptions for 88 yards and a touchdown. He also had a leaping catch for a two-point conversion pass from rookie quarterback C.J. Beathard.

“I was locked in and ready to go,” Bourne said. “I studied real hard because I knew I was going to be in the game. I didn’t want to make the same mistakes. That’s what practice is for.”

Bourne (6 foot 1, 203 pounds) played four seasons at Eastern Washington and caught 79 passes for 1,201 yards and seven touchdowns during his senior season. He was overshadowed by college teammate Cooper Kupp, a third-round pick of the Los Angeles Rams.

At the NFL Scouting Combine, Bourne’s 40-yard dash time of 4.68 was one of the slowest times among the 58 wide receivers invited. But only three wide receivers ran a faster three-cone drill (6.73 seconds). He is not a speedster, but he has short-area quickness.

The 49ers signed Bourne as an undrafted rookie. Shanahan said the 49ers gave no consideration to Bourne’s lack of availability for the offseason program before signing him.

“I think that’s stuff you talk more about with a drafted guy,” Shanahan said. “But when it comes to trying to sign a guy after the draft, you’re trying to just look at the most talented guys that didn’t get drafted and you’re doing whatever you can to get them into your building.”

Bourne and Beathard teamed up on impressive back-to-back plays in the 49ers’ 27-17 victory over the Chiefs in the exhibition opener.

Bourne said he was supposed to begin his route outside of the cornerback on the left side. But the corner was aligned in a way that made it difficult to get to the outside. Bourne went inside. Beathard immediately recognized the improvised route, but still managed to find Bourne open for a 46-yard touchdown pass.

“He’s a really talented receiver,” Beathard said. “He’s skilled and just being able to work with him for the little bit of time we’ve had, it’s nice having him in there, making good catches.”

On the next play, Beathard and Bourne connected on a fade route for the two-point conversion.

“Actually, I was struggling in practice with it a lot,” said Bourne, who has a 34-inch vertical leap. “I haven’t completed one in weeks, and it was a good ball, good timing. I actually didn’t even get a good release. I was fighting with the DB (rookie J.R. Nelson) and had more body control with him and came down with it.”

Bourne faces a difficult challenge to win a roster spot with the 49ers, but he could be placing himself in prime position for the 10-player practice squad.

“He’s got a natural ability to separate and he’s got good hands,” Shanahan said.

“He missed a whole offseason, basically, not counting the rookie minicamp. So that’s had him behind. You’ve got to be the right type of guy to really catch up on that because it’s just impossible to get the same reps as everyone else has.”