The Coca-Cola 600 ran more than one-quarter in the books before the caution flag for the first time for debris on the race track.
A trio Ford drivers have dominated clean race thus far, leading all 114 laps. Aric Almirola and Marcos Ambrose swapped the lead early before point leader Greg Biffle asserted himself as the dominant force in the pre-dusk run of NASCAR's longest race.
Ambrose ran second ahead of Kyle Busch, Jimmie Johnson, and Kasey Kahne. Clint Bowyer, Mark Martin, Brad Keselowski, Jeff Gordon, and Denny Hamlin rounded out the top-10.
Almirola had dropped steadily after starting from the pole position, backsliding to 17th before the caution flag flew. The Tampa native is seeking to give Richard Petty's famous No. 43 its first victory since John Andretti won at Martinsville in 1999. Almirola is also looking for his first true win in either of the top-two divisions in NASCAR. He officially won a Nationwide Series race at Milwaukee in 2007, but Denny Hamlin actually completed the event after the car's sponsor demanded that Hamlin - delayed by traffic and thus kept from starting the race as scheduled - be put into the car during a pit stop.