Ryan Newman, a non-playoff driver, was fastest in the first of two Cup practice sessions Saturday morning at Las Vegas Motor Speedway.
Newman posted a top speed of 183.892 mph around the 1.5-mile track.
Clint Bowyer (playoffs) had the best 10-lap average at 181.010 mph.
Byron recorded the most laps in the session with 39.
Final practice is scheduled for 3:30-4:20 p.m. ET on NBCSN.