New York - Serena Williams struggled but advanced to the fourth round of the US Open on Friday by defeating 101st-ranked compatriot Bethanie Mattek-Sands 3-6, 7-5, 6-0 at Arthur Ashe Stadium.
The 33-year-old American, trying to complete the first calendar Grand Slam since Steffi Graf in 1988, battled nerves and mistakes plus a determined rival, but seized command late in the second set and dominated to the finish.
Williams, holder of all four major titles, is trying for her 22nd career Slam singles crown to match Graf's Open Era record and move two shy of Australian Margaret Court's all-time mark.
Next up for Williams is US 19th seed Madison Keys, who ousted Polish 15th seed Agnieszka Radwanska 6-3, 6-2.
World number one Williams smashed 53 winners against 28 unforced errors, but half those errors came in the first set.
And the three-time defending champion squandered 15 of 21 break-point chances, going 1 of 7 in the first set and 2 of 9 in the second set, while Mattek-Sands capitalized on her first three over the first two sets.
"Yes I did," Williams said matter-of-factly when told she missed many break point opportunities.
"But I said, 'Serena, just keep going. Here's another one. Keep trying.'"
Williams connected only 52 percent of first serves in the first set but was near 70 percent the rest of the way and won 81 percent of her first-serve points in all.
"It's not where I want it but it's getting better," Williams said. "I hope to be in this tournament for a little bit so hopefully it will get better."
Mattek-Sands took a 3-0 lead, sent a forehand volley long in the fifth game to give Williams a break, but then broke back in the sixth for a 4-2 edge and held twice to claim the opening set.
Williams went to third sets nine times in 23 prior Grand Slam matches this year and won them all. She had lost the first set twice at the Australian Open, four times at the French Open and once at Wimbledon, and just as in those tension-packed moments she found her form in New York.
Fighting her nerves most of the second set, Williams broke for a 5-3 lead. Mattek-Sands answered, breaking back on a forehand winner with help from two Williams double faults and holding to 5-5.
But Williams held at love with her fifth ace and broke for the set in the 12th game when Mattek-Sands hit a backhand long.
Williams grimaced and nearly slammed her racquet when she didn't break on her first chance in the last game.
And after the set, she waved off a television camera that got too near, saying, "I don't want that there."
Williams then breezed through Mattek-Sands in only 25 minutes, on overhead smash ending matters after one hour 49 minutes.
US Open results on Friday, the fifth day of the 2015 tournament
at Flushing Meadows (x denotes seeded player):
Novak Djokovic (SRB x1) bt Andreas Seppi (ITA x25) 6-3, 7-5, 7-5
Roberto Bautista (ESP x23) bt David Goffin (BEL x14) 2-6, 5-7, 6-3, 3-1 -
Feliciano Lopez (ESP x18) bt Milos Raonic (CAN x10) 6-2, 7-6 (7/4), 6-3
Fabio Fognini (ITA x32) bt Rafael Nadal (ESP x8) 3-6, 4-6, 6-4, 6-3, 6-4
Benoit Paire (FRA) bt Tommy Robredo (ESP x26) 7-6 (7/3), 6-1, 6-1
Jo-Wilfried Tsonga (FRA x19) bt Sergiy Stakhovsky (UKR) 6-3, 7-5, 6-2
Marin Cilic (CRO x9) bt Mikhail Kukushkin (KAZ) 6-7 (5/7), 7-6 (7/1), 6-3,
6-7 (3/7), 6-1
Jeremy Chardy (FRA x27) bt David Ferrer (ESP x7) 7-6 (8/6), 4-6, 6-3, 6-1
Serena Williams (USA x1) bt Bethanie Mattek-Sands (USA) 3-6, 7-5, 6-0
Madison Keys (USA x19) bt Agnieszka Radwanska (POL x15) 6-3, 6-2
Venus Williams (USA x23) bt Belinda Bencic (SUI x12) 6-3, 6-4
Anett Kontaveit (EST) bt Madison Brengle (USA) 6-2, 3-6, 6-0
Kristina Mladenovic (FRA) bt Darya Kasatkina (RUS) 6-2, 6-3
Ekaterina Makarova (RUS x13) bt Elina Svitolina (UKR x17) 6-3, 7-5
Roberta Vinci (ITA) bt Mariana Duque (COL) 6-1, 5-7, 6-2
Eugenie Bouchard (CAN x25) bt Dominika Cibulkova (SVK) 7-6 (11/9), 4-6, 6-3