Williams took advantage of a poor serving performance by Muchova and broke her opponent five times, including in the final game where she sealed the victory.
Serena Williams moved another step closer to a record-tying 24th career Grand Slam title with a comfortable 6-3 6-2 victory over Czech Karolina Muchova on Friday to reach the last 16 at the U.S. Open.
Wimbledon quarter-finalist Muchova held serve for an early 3-2 lead in her first career meeting with Williams but the six-times champion cranked up the pace and won the next seven games to take over the match.
“I think I had a lot of intensity today which was really good for me,” Williams, who improved to 18-1 in third-round U.S. Open matches, said in her on-court interview.
Williams took advantage of a poor serving performance by Muchova and broke her opponent five times, including in the final game where she sealed the victory when the Czech sent a forehand long.
Muchova, who reached the U.S. Open third round last year as a qualifier in her Grand Slam main draw debut, won just 36% percent of points on her second serve, which Williams feasted on with her trademark power.
The victory for Williams was a much smoother outing than she had in her previous match, where she spent the first half of the encounter trying to find her rhythm against American teenager Catherine McNally.
Williams made 28 unforced errors against McNally and later promised to be better, a claim which she backed up as she made only 15 unforced errors in her clash with Muchova.
Up next for Williams will be Croatian 22nd seed Petra Martic, who beat Latvian Anastasija Sevastova.
Martic is in the midst of a breakthrough season in which she claimed her first title with a triumph in Istanbul and followed that up with an impressive run at the French Open where she reached her first Grand Slam quarter-final.