New York: World number one Serena Williams shook off a woeful start Wednesday to advance her quest for tennis history while Rafael Nadal joined her in the third round of the US Open.
Williams, trying to complete the first calendar Grand Slam singles sweep since Steffi Graf in 1988, defeated 110th-ranked Dutch qualifier Kiki Bertens 7-6 (7/5), 6-3 at Arthur Ashe Stadium despite 34 unforced errors and 10 double faults.
"I just kept fighting for each point, not for a lot but just one at a time," Williams said.
"I had been pretty relaxed. Today I was a little tight. I think it showed. Hopefully I can get back to where I was before."
The 33-year-old American, trying to match Graf`s Open Era record of 22 career Slam singles titles and win an Open Era-record seventh US Open crown, improved to 50-2 on the year and sustained her march toward history.
Spanish eighth seed Nadal, a 14-time Grand Slam champion, ousted Argentina`s Diego Schwartzman 7-6 (7/5), 6-3, 7-5, while top-ranked Novak Djokovic, on a last-eight collision course with Nadal, played later against Austrian Andreas Haider-Maurer.
Three-time defending champion Williams, the oldest women`s Slam winner, completed her second "Serena Slam" of four major wins in a row by winning the Wimbledon crown in July.
Williams broke back to level at 5-5 in the first set but double faulted four times in the 11th game before holding, then fell behind 4-0 in the tie-break before rallying largely on Bertens` unforced errors.
"It definitely doesn`t worry me, being down a lot," Williams said. "I know I can make a comeback, make a run for it."
But her form was so shocking that Williams ran to the practice courts to work on serves after the match.
Next up for Williams will be fellow American Bethanie Mattek-Sands, who beat compatriot CoCo Vandeweghe 6-2, 6-1.
"I`ll have to play a little better if I want to win," Williams said.Nadal was down 5-4 in the first set tie-breaker before battling back against Schwartzman.
"Happy to be through," Nadal said. "Was a tough battle. I feel lucky to be through.... To take that first set was very important to me."
Nadal, the 2010 and 2013 US Open champion, improved to 22-1 in his past 23 US Open matches after missing 2012 and 2014 due to injury and finishing as the 2011 runner-up.
Defending champion Marin Cilic and seventh seed David Ferrer moved nearer a round of 16 meeting.
Croatian ninth seed Cilic fired 19 aces in defeating 139th-ranked Russian qualifier Evgeny Donskoy 6-2, 6-3, 7-5.
"It`s sort of unreal. I was working all my life to win a Grand Slam and now I`m working to defend one," Cilic said.
Spain`s Ferrer, the 2013 French Open runner-up who missed the past 2 1/2 months with an elbow injury, downed 102nd-ranked Serb Filip Krajinovic 7-5, 7-5, 7-6 (7/4).
"I`m very happy I`m in the third round," said Ferrer. "It`s a nice comeback playing on these courts."Serena Williams could reach a Grand Slam singles final without facing a top-10 rival for the first time in her career, but her quarter-final foe could be 35-year-old sister Venus or Swiss 18-year-old Belinda Bencic, who inflicted Serena`s most recent defeat.
Bencic, the highest seed remaining in Williams` half of the draw at 12th, saved three match points in the second set and outlasted Japan`s 88th-ranked Misaki Doi 5-7, 7-6 (7/3), 6-3.
"I`m just happy I could turn it around," she said.
Bencic, who defeated Serena Williams in the Toronto semi-finals last month, next plays Venus after the elder Williams eliminated fellow American Irina Falconi 6-3, 6-7 (2/7), 6-2.
"She played really well in the tie-breaker," Venus Williams said. "In the third set I had a lot more clarity."
Australian Open semi-finalist Madison Keys ripped 100th-ranked Czech Tereza Smitkova 6-1, 6-2. The American 19th seed hopes for a fourth-round date with Serena Williams, who ousted her in Australia.
"Fingers crossed it could happen. If it does happen I could come out and have some fun at my home Slam," Keys said.
Canadian 25th seed Eugenie Bouchard advanced over Slovenia`s Polona Hercog 6-3, 6-7 (2/7), 6-3, to reach round three. She had not won back-to-back matches since March.
"She was tough getting balls back but I held my nerve at the end which I thought was the key to the match," Bouchard said. "I`m excited to win two matches in a row."