Six-time champion Serena Williams is safely through to the fourth round of the US Open after a routine victory over Czech Karolina Muchova.

The American won 6-3 6-2 after converting five of nine break points against the Wimbledon quarter-finalist.

Williams was broken back midway through the second set but it was an otherwise flawless display.

Second seed Ashleigh Barty is also through after a 7-5 6-3 win over Greek 30th seed Maria Sakkari.

And third seed Karolina Pliskova overcame a mid-match blip to beat Tunisia's Ons Jabeur 6-1 4-6 6-4.

The Czech 2016 finalist had been a set and a break up and had appeared to be cruising before Jabeur took a medical timeout early in the second set and won five games in a row to make a match of it.

Pliskova will face British number one Johanna Konta in the fourth round after the 16th seed defeated China's Zhang Shuai 6-2 6-3.

They are joined in the fourth round by Ukrainian fifth seed Elina Svitolina, who beat compatriot Dayana Yastremska 6-2 6-0 in just 54 minutes.

She will face 10th seed and 2017 runner-up Madison Keys, who battled past fellow American Sofia Kenin 6-3 7-5 after taking a medical timeout in the second set because she "did not feel 100%".

She had been cruising but her level dropped in the second set and she had her pulse and blood pressure checked while trailing 4-3. But she continued playing and went on to get a decisive break in the 11th game before serving out the match.

Meanwhile, Australian French Open champion Barty will take on Chinese 18th seed Wang Qiang or France's Fiona Ferro.

Williams, who is still seeking to equal Australian Margaret Court's all-time record of 24 Grand Slam singles titles, will play Croatian 22nd seed Petra Martic in round four.

Martic, a French Open quarter-finalist, defeated Latvian 12th seed Anastasija Sevastova 6-4 6-3 on court 10.