"I'm really happy with how I served -- I had to retire from my last match because of my shoulder thing, so I wasn't really sure how I was going to serve today," she said. "But I was told I hit 16 aces, so that's pretty good for me." Sixth-seeded Dutchwoman Kiki Bertens also progressed in three sets, beating Ukraine's Dayana Yastremska 6-4, 1-6, 6-3.