Garbine Muguruza out of China Open tennis - at 2:31 am

China Open organisers faced questions after two-time Grand Slam champion Garbine Muguruza lost in a match which did not start until nearly 1:00 am and concluded at 2:31 am Sunday.

The Spaniard's conqueror Sofia Kenin said that she felt "mentally drained" following the late-night first-round encounter in Beijing, which the American won 6-0, 2-6, 6-2.

"I obviously started out really well in the first set and I knew that she was going to pick up her game," the 15th seed told the official WTA website.

"I just felt pretty tired, mentally drained, but I'm happy that I somehow found a way to just fight through it.

"The support from the crowd was great, even at 2:30 in the morning, surprisingly," added the Moscow-born Kenin.

Her clash with Muguruza, 25, who won the 2016 French Open and Wimbledon a year later, was delayed after all four previous matches on the main Diamond Court went to three sets.

AFP has approached the China Open for comment about its scheduling.