Chinese star Liu Xiang clocked 13.09 seconds in winning the 110m hurdles at the IAAF World Challenge meeting in Kawasaki, Japan on Sunday.
Despite heavy rain, the 2004 Olympic gold medallist finished nearly a quarter of a second ahead of second-placed American Omo Osaghae.
"It was my first outdoor race," said Liu, who won world indoor silver over the 60m hurdles in Istanbul in March.
"The track was wet and the wind was strong, but I am satisfied with my time."
Three-time world 200m champion Allyson Felix won the 100m in 11.22sec, saying she did not yet know whether she would race the 200 and 400m at the London Olympics.
"I know where I am now and what I need to improve, so I am excited to start working on things," the American said.
Reigning women's 400m champion Amantle Montsho of Botswana dominated her season's second outing over the one-lap discipline, clocking 50.52sec to finish more than a second ahead of Joanne Cuddihy.
"I had a great race even though the weather was bad," Montsho said.