Olympic champion Kirani James powered to victory against his controversial predecessor and his main rivals from London 2012 in the 400m at Shanghai's Diamond League meeting.
But 110m hurdles Olympic champion and world record holder Aries Merritt was given a scare in a world championship season when he pulled up with an apparent injury after just three strides.
As Merritt called it quits at the first hurdle, American compatriot and reigning world champion Jason Richardson streaked to victory in 13.23 seconds.
Merritt said after the race that he had a "small cramp" and decided to pull out rather than risk a serious injury.
American Ryan Wilson finished second, while China's emerging hurdling talent Xie Wenjun came third with a personal best time of 13.28 seconds.
Many sports fans in China hope the 22-year-old will follow in the footsteps of Liu Xiang, who has been forced out of the season with injury, with some reports in China doubting if he will return.
Liu became a national hero when he claimed China's first Olympic track and field gold at Athens in 2004, but then suffered injury heartbreak in the Beijing and London Games.
In the 400m, Grenada's James raced ahead on the final bend to edge out 2008 Olympic champion, American Lashawn Merritt, into second place.
Luguelin Santos of the Dominican Republic, the silver medallist from last summer's Games, was third, more than a second behind James, who crossed the line at a season's best 44.02.
Merritt would have been well known to fans in a damp Shanghai Stadium after claiming gold at the showcase Beijing Olympics.
But he has endured a torrid time after the 2008 Games, serving a ban for a positive doping test that he blamed on a "male-enhancement product".
He successfully challenged the IOC's ban on former drug users to compete in London, only to pull out injured during the heats.
"Considering it was my first 400m this year, I am still getting familiar with the game," Merritt said. "So I feel not bad about the result. It's a long season and it's just beginning."
Russian pole-vault queen Yelena Isinbayeva went some way to overcoming her Olympic disappointment with a strong performance.
Isinbayeva, who last week said she was contemplating retiring after the August 10-18 world championships in Moscow, Russia, won her event with a jump of 4.70 metres.
The multiple record breaker, who failed to become the first woman in history to achieve three successive Olympic gold medals when she came third in London, turned down any further vaults with what looked like a sore ankle.
In another re-run between gold and silver medallists from London 2012, Jamaica's Shelly-Ann Fraser-Pryce claimed victory in the 100m in a season's best of 10.93 seconds ahead of rival Carmelita Jeter, with the American settling for third place behind Nigerian Blessing Okagbare.
"I feel very relaxed. I came here to win and just see how I would do," said Fraser-Pryce, who confirmed she would go for the sprint double at the Moscow worlds.
One standout performance of the night came from a home hope, Li Jinzhe, in the long jump.
Li leaped to a world leading distance of 8.38 metres to finish ahead of Russian Aleksandr Menkov (8.31 metres) and Britain's Olympic champion Greg Rutherford (8.08 metres).