DARLINGTON, S.C. – Martin Truex Jr. already has won two of NASCAR's most coveted races. Now he's seeking a much bigger honor.

Truex led the final 28 laps and held off the Kevin Harvick's powerhouse car to win the Southern 500, closing the summer season with a second of Sprint Cup's "crown jewel" races on Labor Day weekend. He began things by winning at Charlotte Motor Speedway on Memorial Day weekend.

Truex stamped himself as a contender to be reckoned with when the Sprint Cup playoffs start in two weeks.

"We're hungry. We're working hard," Truex said. "This is just the beginning for us, I think."

Many others think that, too, especially after Truex patiently stayed in the top 10 throughout and pounced when the opportunity struck, moving past leader Ryan Newman and never surrendering the top spot.

It was Truex's fifth NASCAR victory and first in 11 career Darlington races.

Martin Truex Jr.:  Posted his second win of the season and fifth of his career.

Crew chief Cole Pearn said winning two crown jewel races in a season is something special, but the team's focus is on the championship Chase that starts at Chicagoland Speedway in two weeks.

"You've got to take the highs when they're here and then get back to work," he said.

Truex pulled up to the inside wall to greet his crew after the win, then took off for some celebration donuts at the track "Too Tough To Tame."

Harvick, who led 214 of 367 laps, had words for his crew, too — much angrier and pointed about their poor performance in the pits. During one 16.6-second stop, Harvick fell from first to 12th and, though he got to back to second, correctly said on the radio after that stop, "It's pretty much over at this point."

The 2014 Sprint Cup champion said it was time for the crew to perform: "I'm over being a cheerleader. Those guys get paid a lot of money to perform on pit road, and cheerleading really hasn't been working."