Serena Williams struggled but moved nearer to the first calendar Grand Slam since 1988 by defeating Dutch qualifier Kiki Bertens 7-6 (7-5) 6-3 at the US Open.
World No.1 Williams, a three-time defending champion seeking her seventh US Open title overall, was outplayed early by her 110th-ranked rival at Arthur Ashe Stadium.
But Williams overcame 34 unforced errors and 10 double faults to win and sustain her march toward history.
"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 is trying to complete the first calendar grand slam since Steffi Graf in 1988 and equal Graf's Open Era record of 22 slam singles titles, two shy of Australian Margaret Court's all-time record.
Williams completed her second "Serena Slam" of four major wins in a row by winning the Wimbledon crown in July and the 33-year-old American can claim her Open era-record seventh US Open title as well as extend her mark as the oldest woman Slam champion.
Bertens nearly derailed all those dreams, with more than a little help from Williams.
Next up for Williams will be 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.
With three top-10 seeds on Serena's side of the draw losing openers and third seed Maria Sharapova withdrawing due to injury, Williams could reach a grand slam singles final without facing a top-10 rival for the first time in her career.
Swiss teen Belinda Bencic, the highest seed remaining in Williams' half of the draw at 12, faces Japan's 88th-ranked Misaki Doi later.
Bencic, who defeated Williams in the Toronto semi-finals last month, could play Serena's older sister, Venus, who meets fellow American Irina Falconi later, in the third round.
Either Bencic, 18, or Venus, 35, could meet Serena in the quarter-finals.
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.
AFP
