American wild card Riske routs seventh-seeded Kvitova at U.S. Open Serena Williams and Sloane Stephens are through to a highly anticipated matchup in the round of 16 at the U.S. Open, where they're joined by a less expected American, Alison Riske. Maybe's Riske's run isn't that much of a surprise considering her recent surge. The 23-year-old Pittsburgh native came into the summer having never accomplished any of these feats: winning a match in a Grand Slam tournament, at a WTA Tour event on hard courts, or against at top-10 foe. She's now achieved all that, her latest breakthrough victory a rout of 2011 Wimbledon champ Petra Kvitova on Saturday. Riske won 6-3, 6-0, taking the last eight games against the seventh-seeded Czech. "I've got a new confidence in myself," Riske said through tears in an on-court interview. I believe that I belong here. She was 0-5 at major tournaments before Wimbledon this year but is 5-1 since. Riske just broke into the top 100 in late July; now she'll likely earn a top-60 ranking. She has always thrived on grass, making the third round at Wimbledon this year. Now she's starting to figure out the hard courts. Kvitova, who called for a trainer before the final game, had seven double-faults and 27 unforced errors. She has long struggled at Flushing Meadows, the only major tournament at which she hasn't made the semifinals. Williams advanced after midnight Saturday morning, beating 78th-ranked Yaroslava Shvedova of Kazakhstan 6-3, 6-1. The previous match in Arthur Ashe Stadium on Friday night lasted more than four hours: 2001 U.S. Open champion Lleyton Hewitt's 6-4, 5-7, 3-6, 7-6 (2), 6-1 comeback victory over 2009 champion Juan Martin del Potro. Much, much earlier, Stephens reached the round of 16 in New York for the first time by beating 23rd-seeded Jamie Hampton 6-1, 6-3 in another all-American matchup. Ever since Stephens announced her presence as a major force with a quarterfinal victory over a hobbling Williams at the Australian Open, tennis fans have craved a rematch on the biggest stage. Now it's here. Saturday's session opened with two minor upsets: Simona Halep, seeded 21st, crushed No. 14 Maria Kirilenko 6-1, 6-0, and Flavia Pennetta beat 27th-seeded Svetlana Kuznetsova 7-5, 6-1.