Nemechek led 49 of 200 laps and extended his streak to seven years with at least one Busch series victory. This was his 13th career win on the circuit.
Todd Bodine had the lead with 32 laps to go. Racing side-by-side with Nemechek, Bodine slid through the grass on the frontstretch and Nemechek inherited the lead.
"I don't know what was going on there," Nemechek said. "He was underneath me and went up high and I tried to crowd him. I don't know if he lost a tire or what, but he got loose there."
Bodine finished 19th.
Harvick led the first 81 laps and 93 all together. The Winston Cup regular grabbed the Busch series lead, 55 points ahead of David Green who finished sixth in the only Pontiac Grand Prix among the top 10.
Mike Bliss was third for the best finish of his Busch series career and Steve Park made it a sweep of the top four positions for Chevrolet Monte Carlos.
Park overcame a spin as he competed in his first Busch race since suffering serious injuries in 2001 at Darlington Raceway.
Jason Keller started second and rounded out the top-five finishers with the top Ford Taurus.
Daytona 500 champion Michael Waltrip started 40th but made it to the front before a rain delay halted the race on lap 141. He ended up seventh.
Pole-sitter Stanton Barrett, a Hollywood stuntman when not racing, was eighth. He gained the top starting position based on 2002 owner points after qualifying was rained out Friday. Barrett drives a Ford for Roush Racing.
Defending champion Jeff Burton was running second when his Ford caught fire on lap 116. The fire created thick black smoke, but Burton exited the car unharmed. He placed 35th.
"An oil line must have broken or come loose or something because we were sitting there running and the thing was really, really fast," Burton said. "Then, all of a sudden it really picked up a bad push and I thought a tire was going down, so I kind of slowed down. Next thing I know, I looked in the mirror and there's fire coming out from under it."