Serena Williams had few problems with Karolina Muchova but had to overcome frustrations with her serve in her third-round match. The six-time US Open champion ultimately overpowered her Czech opponent running out a 6-3, 6-2 victor in 73 minutes. This was far from a complete game from Williams though who served seven double faults including two in the fifth game of the second set which gave Muchova her only break. In her following service game, Williams theatrically gestured to the sky in thanks after serving an ace with the first point. From this point onwards she had few problems in finishing off her opponent. Williams will now play Petra Martic in the last 16, after the Croatian beat Anastasia Sevastova in straight sets. "It's another player that comes to the net a lot that plays a lot of slices, it's going to be interesting," Williams said.