It didn't take long to find out Saturday in the Xfinity Series Irish Hills 250 at Michigan International Speedway.
Busch, who started on the pole, tried to slide up in front of Keselowski shortly after the green flag, before they got to Turn 1. Busch went spinning into the inside grass.
Busch's car suffered significant damage but rallied to finish fifth, while Keselowski's car suffered a little bit of front-end damage that didn't keep him from winning the opening stage before he eventually finished fourth. Denny Hamlin won the race.
It was obvious Busch wasn't happy with Keselowski, with whom he has had several run-ins over the years. When asked what happened, Busch said, "It's not the first time."
Should Keselowski have given him more room, considering it was the first lap? Busch: "No question."
Keselowski seemed surprised that Busch tried to slide up in front of him, theorizing that maybe Busch didn't know he was there.
"I lifted the best I could -- I guess I just didn't do a good enough job lifting," Keselowski said. "I was already pulling up beside him. There's only so much I could lift. I guess I maybe could have done a better job.
"I had a big run, and I tried to go to the bottom and tried to go to the top. And there was only so many places to go on the race track."
Much like Keselowski, Busch didn't say anything too fiery as he walked to the garage following the race.
"I don't know [what happened]," Busch said. "I hate it happened. I got something out of it."
Get something out of it, he did. Busch battled an ill-handling car throughout the race -- no surprise considering the significant right-side rear damage to the car -- and used some late restarts to break into the top 5.
"The car was the biggest piece of ... out there, and I made something happen with it," Busch said. "That's what happens when you put a driver like me out there."
While Keselowski challenged for the win throughout the day, he saw the hole in the front of his car afterward and didn't think he came out of that first-lap contact unscathed.
"I don't think anybody really won on that one," Keselowski said.
Hamlin, who started sixth, said the battling for position on the first lap of a 125-lap race indicated how important each spot matters on each lap.
"That just tells you when they're fighting that hard into Turn 1 on the first lap, track position is a major, major key," Hamlin said.