Keselowski won the crash-filled race at the Memphis Motorsports Park by overcoming a bump with Busch near the finish line, beating him by less than 1 second.
The race featured 14 caution flags due to numerous crashes involving, among others, Eric McClure, Carl Edwards and Michael McDowell.
"It felt like I was getting nudged all the way around," said Keselowski, who received a $25,000 bonus after his fourth victory this season and sixth in his Nationwide career. (But) that's short track racing."
"I should be happy with … a second-place finish," Busch said. "We didn't have the car. (I) lost a lot of money today."
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