Valentino Rossi lapped quick enough to be in the top half of the NASCAR Nationwide Series field as he tried Kyle Busch's Toyota stock car in a promotional event on Monday.
Seven-time MotoGP champion Rossi travelled to Charlotte Motor Speedway after finishing sixth in his series' inaugural Austin race on Sunday.
Busch was impressed by the speed Rossi eventually reached, as he lapped in the 185mph region.
"I thought he did pretty good," said Busch, the most successful driver in Nationwide history with 55 career wins.
"He started out a little slow, which is fine, but every lap he picked it up a lot.
"He got to where he was running some competitive lap speeds - times that would put him in the top 15 in Nationwide Series practice.
"That's pretty good for a guy in his first start, who is just coming over and getting used to things and someone that is used to driving on two wheels."
Rossi said the experience had been disconcerting at first, but that he had hugely enjoyed it.
"I have a lot of friends from Europe and Italy who follow NASCAR," he said.
"It looks like it's a completely different type of racing than what we do in Europe and I expected something more like this - exciting, high speed and a great feeling in the corner. On the banking you have a lot of grip, so you are glued on the racetrack.
"At the beginning it was a bit strange because it's difficult to go straight.
"But after some laps, I had a lot of confidence and I was able to go faster and faster and faster."