DARLINGTON, S.C. — Martin Truex Jr. has already 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 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 at Darlington Raceway.

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,’’ Pearn said.

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

Harvick, who led 214 of 367 laps, had some 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.

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,’’ he said. ‘‘You've got to get after it on pit road and do your job.’’

Last week’s winner at Michigan, Kyle Larson, finished third, and Denny Hamlin was fourth. Joey Logano was fifth.

It’s the second time in the past six Southern 500s that single-car Furniture Row Racing wound up in victory lane. Regan Smith stunned the Sprint Cup garage in 2011 with his win here.

Truex, among the four finalists in last year’s championship Chase, is locked in again this year and has stamped himself a significant contender for the Sprint Cup crown.

‘‘It was definitely worth the wait,’’ he said.