NEW YORK • Shortly after winning a surprisingly competitive second-round match against Kiki Bertens that lasted 1hr 32 min, Serena Williams and her coach went back to the practice court for almost an hour.
They worked on her serve which was a source of frustration in the match. The world No. 1 also fired passing shots down the lines that screamed off her racket at a ferocious pace.
Against Bertens on Wednesday, she made 34 unforced errors, double-faulted 10 times and won only 36 per cent of the points on her second serve.
Hence, the extra workout after the 7-6 (7-5), 6-3 victory for the American. She was broken in her first service game and did not break back until the world No. 110 was serving for the set at 5-4.
Bertens also led 4-0 in the tiebreaker but crumbled.
After that, the ending was inevitable and Williams' bid to complete the first calendar Grand Slam singles sweep since Steffi Graf in 1988 remained intact. However, the 33-year-old was not pleased.
"It definitely wasn't my happiest of moments," she said of coming back to win the opening set.
"I don't think you should be happy with just winning."
She said her coach Patrick Mouratoglou had noticed specific things that needed to be addressed.
At one point during the practice session, he demonstrated the proper shoulder tilt while serving.
In the third round, Williams will play Bethanie Mattek-Sands who routed Coco Vandeweghe 6-2, 6-1.
"I have to start out strong if I want to stay in the tournament," Williams said.
She could reach a Grand Slam singles final without facing a top-10 rival for the first time in her career.
Belinda Bencic, who inflicted her most recent defeat, is the highest seed left in Williams' half of the draw at 12th.
And the 18-year-old barely survived her second-round match.
She saved three match points in the second set before outlasting Japan's 88th-ranked Misaki Doi 5-7, 7-6 (7-3), 6-3.
Her next test? Another Williams in the form of Venus, who will seek out a scouting report from little sister Serena.
"We always give each other advice, especially if one of us has played the other opponent recently," said Venus after beating fellow American Irina Falconi 6-3, 6-7 (2-7), 6-2 .
Defending men's singles champion Marin Cilic, two-time winner Rafael Nadal and world No. 1 Novak Djokovic all eased into the third round with straight sets wins.
After playing his opening match on an outside court, Cilic took his US Open title defence back to a sweltering Arthur Ashe Stadium.
He stormed into the third round with a 6-2, 6-3, 7-5 win over Russian qualifier Evgeny Donskoy.
Nadal got his second-round contest off to a sluggish start but the eighth-seeded Spaniard was quickly in control, dispatching Diego Schwartzman 7-6 (7-5), 6-3, 7-5.
Djokovic demolished Austrian Andreas Haider-Maurer 6-4, 6-1, 6-2 and still had enough energy left to dance on court with an entertainer whose job was to fire up the crowd's mood at Arthur Ashe Stadium during changeovers.
NEW YORK TIMES, AGENCE FRANCE-PRESSE, REUTERS
Day 4: Morning (11pm). Night (tomorrow, 7am) - StarHub Ch201
US Open (2nd rd, selected)
Men: Novak Djokovic (Srb) bt Andreas Haider-Maurer (Aut) 6-4 6-1 6-2, Milos Raonic (Can) bt Fernando Verdasco (Esp) 6-2 6-4 6-7 (5-7) 7-6 (7-1), Feliciano Lopez (Esp) bt Mardy Fish (USA) 2-6 6-3 1-6 7-5 6-3, Rafael Nadal (Esp) bt Diego Schwartzman (Arg) 7-6 (7-5) 6-3 7-5, Tommy Robredo (Esp) bt Samuel Groth (Aus) 6-4 7-6 (7-3) 6-4, Jo-Wilfried Tsonga (Fra) bt Marcel Granollers (Esp) 6-3 6-4 6-3, Marin Cilic (Cro) bt Evgeny Donskoy (Rus) 6-2 6-3 7-5, Mikhail Kukushkin (Kaz) bt Grigor Dimitrov (Bul) 6-3 7-6 (7-2) 2-6 4-6 6-4, David Ferrer (Esp) bt Filip Krajinovic (Srb) 7-5 7-5 7-6 (7-4).
Women: Serena Williams (USA) bt Kiki Bertens (Ned) 7-6 (7-5) 6-3, Madison Keys (USA) bt Tereza Smitkova (Cze) 6-1 6-2, Agnieszka Radwanska (Pol) bt Magda Linette (Pol) 6-3 6-2, Belinda Bencic (Sui) bt Misaki Doi (Jpn) 5-7 7-6 (7-3) 6-3, Venus Williams (USA) bt Irina Falconi (USA) 6-3 6-7 (2-7) 6-2, Anett Kontaveit (Est) bt Anastasia Pavlyuchenkova (Rus) 7-5 6-4, Elina Svitolina (Ukr) bt Kaia Kanepi (Est) 6-3 6-4, Ekaterina Makarova (Rus) bt Lauren Davis (USA) 6-1 6-2, Eugenie Bouchard (Can) bt Polona Hercog (Slo) 6-3 6-7 (2-7) 6-3.