Rome - LJ Van Zyl of South Africa won the men's 400 meters hurdles in 47.91 seconds to extend his impressive start to the season, while European champion David Greene of Britain was second in 48.24 at the at the star-studded Golden Gala on Thursday.
In Doha earlier this month, Van Zyl beat last year's Diamond League race winner Bershawn Jackson.
On the women's side, American standout Allyson Felix improved her season-best time in the 400 meters while world champion Sanya Richards-Ross struggled to a fifth-place finish.
Felix is the three-time defending world champion in the 200 meters but has shown this year that she could be just as big a threat in the 400 meters at the Aug. 27-Sept. 4 worlds championships in Daegu, South Korea.
Felix clocked 49.81 seconds to improve on the 50.33 she ran at this year's opening Diamond League meet in Doha, Qatar, this month.
Amantle Montsho of Botswana was the runner-up in 50.47 and Francena McCorory of the United States crossed third in 50.70.
Richards-Ross, who missed most of last year with a quadriceps injury, clocked 50.98. She shook her head in disappointment at the finish, although she improved on the 51.62 she clocked in Kingston, Jamaica, earlier this month.
Felix won four of four Diamond League 400s last year but never broke the 50-second barrier.
She and Richards-Ross were slated to race again 45 minutes later in the 200 meters.
Also later, world record-holder Usain Bolt faces former holder Asafa Powell, European champion Christophe Lemaitre, and Olympic silver medalist Richard Thompson in a stacked 100-meter race.
This was the third meeting of the Diamond League circuit, with the next stop scheduled for Eugene, Oregon, on June 4.World champion Brittney Reese led the long jump with a season-best 6.94, while fellow American Funmi Jimoh - who beat Olympic champion Maurren Maggi in Doha - settled for second at 6.87.
Meanwhile, local favorite Andrew Howe of Italy got the crowd going by winning the 200 in 20.31 seconds. The 2007 long jump silver medalist, Howe is focusing on the 200 at the start of the season, but will compete only in the long jump at worlds due to a schedule conflict.