AGENCIES: 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.