Murray loses in opening round at US Open tuneup

Grigor Dmitrov, the defending champion who is seeded fifth, was not entirely upset about Nadal's absence.

"When Rafa is missing, he's missed, not so much by the players as much as the fans," he said. "All joking aside, I love spending time with Rafa and practicing with him and playing with him. I would be the last person to say I wouldn't want to play with him."

Monday's first full day of main-draw competition opened with 13th-seeded Madison Keys holding off Bethanie Mattek-Sands 3-6, 7-6 (3), 6-4 to reach the second round. Wild-card Victoria Azarenka, a two-time Australian Open champion, also came from behind to beat Carla Suarez Navarro 6-7 (5), 6-2, 6-4.

Tenth-seeded Julia Goerges was losing to Kristina Mladenovic 6-4, 3-2 when she retired because of a lower left leg injury. Advancing were Lesia Tsurenko, wildcard Svetiana Kuznetsova, qualifier Viktoria Kuzmova and Anett Kontaveit.

On the men’s side, Sam Querrey ground out a 6-4, 6-7 (5), 7-6 (5) win over fellow American John Isner. Querrey gained an edge with a mini-break on the fifth point of the second tiebreaker when Isner sailed a forehand wide of the backhand sideline. Querry closed out the 2-hour, 7-minute match with an ace that survived an Inner challenge.

Kei Nishikori beat Andrey Rublev 7-5, 6-3, and 13th-seeded Pablo Carreno Busta topped Richard Gasquet 6-3, 2-6, 6-3. Other winners were Leonardo Mayer, Jeremy Chardy, Benoit Paire, Peter Gojowczyk, Denis Shapovalov and qualifier Bradley Klahn.