NEW YORK – It took three days for the men at the U.S. Open to complete their first round of singles; that's the way it's scheduled and luckily the weather was cooperative, if a bit toasty.
Now they've joined the women in the second round. Here are some of the matches to keep an eye on.
MATCHES TO WATCH: MEN
Sam Querrey (USA) vs.  Guillermo Garcia-Lopez (ESP): On paper, the American is quite capable of upsetting the seeded player and moving onto the third round. But with Querrey during the last year or two, it's been hard to tell whether he can or will play up to his level. It is definitely a potential upset in the making even if Garcia-Lopez, who possesses a terrific one-handed backhand, is as solid as they come.
 Vasek Pospisil (CAN)/Jack Sock (USA) vs Henri Kontinen/Jarkko Nieminen (FIN): The Wimbledon and Atlanta champions are a question mark going into this one after Sock was forced to retire from his first-round singles match with a calf strain. A couple of days of rest and treatment might do the trick, though, as the popular, exciting young duo tries to win another Grand Slam. His partner, Pospisil, had a shoulder injury that hampered him in his five-set loss in the first round of singles to Simone Bolelli of Italy.
Steve Johnson, who had to retire from his singles match Wednesday with severe cramping, also is scheduled to play doubles, with Sam Querrey
MATCHES TO WATCH: WOMEN
Catherine Bellis (USA) vs. Zarina Diyas (KAZ): After the whirlwind of emotion and attention following the 15-year-old American's upset win over No. 12 seed Dominika Cibulkova of Slovakia in the first round, she must come back to earth against an opponent far less formidable on paper, but still far more experienced and far more highly ranked. At 20, Diyas has just quietly moved into the top 50.
Aleksandra Krunic (SRB) vs.  Madison Keys (USA): This one will be a major contrast in styles. Keys is a tall, strong, big-serving powerhouse. Krunic, 21 and a qualifier, is charitably listed at 5-foot-4 and 117 pounds but runs like the wind.
 Timea Babos (HUN)/Kristina Mladenovic (FRA) vs. Venus Williams/Serena Williams (USA): Because the WIlliams sisters rarely play doubles, they are unseeded and run the risk of playing a very good team in the first round when they do play. Everyone will remember their last doubles effort at Wimbledon two months ago, when a woozy Serena had to be attended to, and the match was forfeited. The Grandstand should be packed for this one, which is scheduled at the end of the day.
Coco Vandeweghe (USA) vs.  Carla Suárez Navarro (ESP): Vandeweghe has had a breakout summer of sorts at age 22. And while Suárez Navarro, who's underrated and has a sweet one-handed backhand so rare in the women's game, can beat anyone on a given day, perhaps the home-country advantage could help Vandeweghe get to the third round.
Sorana Cirstea (ROU) vs.  Eugenie Bouchard (CAN): This will be the first Arthur Ashe Stadium night-match experience for the WTA Tour's new darling, and perhaps the latest start she has ever had to deal with, depending on how late the Andy Murray match goes before her.
In Cirstea, she faces an opponent who, as Bouchard put it after her first-round victory, likes to "whack the ball." The pace won't bother Bouchard; the danger is that Cirstea, who is as capable of having a major off-day as she is of having a day when everything is hitting the lines, could be in a zone.
Americans in singles action
The lack of American men in action, compared to the women, is rather conspicuous. There are just three remaining after the first round of play (two in action Thursday) – the fewest in the tournament's history. At the tournament's start, there were 12.
* John Isner vs. Jan-Lennard Struff (GER)
* Guillermo Garcia-Lopez (ESP) vs. Sam Querrey
* Serena Williams vs. Vania King
* Flavia Pennetta (ITA) vs. Shelby Rogers
* Carla Suárez Navarro (ESP) vs. Coco Vandeweghe
* Victoria Azarenka (BLR) vs. Christina McHale
* Anastasia Pavlyuchenkova (RUS) vs. Nicole Gibbs
* Madison Keys vs. [Q] Aleksandra Krunic (SRB)
*[WC] Catherine Bellis vs. Zarina Diyas (KAZ)
*Varvara Lepchenko vs. Mona Barthel (GER)
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