Kurt Busch was fastest in opening NASCAR Cup Series practice at Darlington with a lap of 171.261 mph (28.714 seconds).
Busch, who also ran the most laps in practice (34), topped fellow Chevrolet driver William Byron, who was second fastest. Byron ran a fast lap of 170.702 mph.
Aric Almirola was third quick at 170.065 mph. Completing the top five was Alex Bowman at 169.988 mph and Jimmie Johnson at 169.660 mph.
Sixth quick was Kyle Larson at 169.478 mph. Larson dominated the Bojangles Southern 500 last season with 284 laps led and both stage wins before fading to a third-place finish. Seventh fastest was Clint Bowyer at 169.164 mph. Ryan Blaney was eighth quick at 168.873 mph.
Ninth on the speed chart was Paul Menard at 168.792 mph. Rounding out the top 10 was Martin Truex Jr. at 168.786 mph.
Defending race winner Brad Keselowski was 19th fastest at 167.618 mph.
There were no incidents in the 50-minute session.
In the best 10 consecutive lap average, it was Byron fastest ahead of Kyle Busch, Bowman, Kurt Busch, Matt DiBenedetto, Denny Hamlin, Erik Jones, Clint Bowyer, Austin Dillon, and Joey Logano.
UP NEXT: Final practice at 4:05 p.m. ET.