Tyson Gay recovered from a poor start to pip fellow American Justin Gatlin and win the Diamond League 100m in Paris in 9.99 seconds.
Gay, beaten by Gatlin at the recent US Olympic trials, came through powerfully ahead of Gatlin, who clocked 10.03, and Frenchman Christophe Lemaitre in 10.08.
Welshman Dai Greene showed he is back to form in the 400m hurdles as he set a new personal best of 47.84 seconds.
Greene was second behind Javier Culson, who won in a world-leading 47.78.
Gay was delighted with his victory, which was a reversal of the result when the sprinters met at the US trials.
"It was a tough race. I knew Gatlin was going to be out and I just tried to come back and get him," he said.
"It's been tough for me, coming back this year. My body and mind are good, I just need to sharpen up and get back in the weight room.
"I think [the Olympic final] will be the most spectacular 100m ever because you have the four, five, six fastest men in history."
World champion Greene, who had a slow start to the season after winter knee surgery, almost chased down Puerto Rican Culson in the final few metres to deliver a strong statement of intent four weeks before the Olympic heats get under way in London on Friday, 3 August.
His new personal best was just 0.02secs outside Kriss Akabusi's 20-year-old British record.
"It's great to get a personal best and it's great to run a fast race again," he said.
"Obviously I had some poor performances at the start of the year and had a tummy bug [before the Diamond League meeting in Rome] where I couldn't race.
"People were slowly losing faith and what I've achieved in the past was slowly being written off.
"I still believed in myself and my coach did also and I think I just proved it tonight. You don't become a bad athlete in a couple of races and the quality always comes through in the end."
Christine Ohuruogu also showed encouraging signs of form a month before she prepares to defend her Olympic 400m title.
The Londoner, 28, has only broken 50 seconds twice - in winning the 2007 World Championships and Olympics gold four years ago.
She never threatened the winner, Amantle Montsho of Botswana in 49.77, but set a season's best of 50.59 secs to finish fourth.
Lisa Dobriskey found the searing pace too hot to handle in the women's 1500m as Moroccan Mariem Alaoui Selsouli outsprinted Turkey's Asli Cakir Alptekin to clock the fastest time in the world this year - 3:56:15 - as she broke the four-minute barrier for the first time.
Dobriskey was eighth in 4:02, but improved her season's best by 10 seconds.
Shara Proctor, who broke the British long jump record in the recent Olympic trials, finished second with a jump of 6.65m in Paris, in a competition won by Russian Yelena Sokolova in 6.70m.
Tiffany Porter enjoyed a good run to finish third in the 100m hurdles in 12.74secs as Australian Sally Pearson won in a new world-leading time this year of 12.40, ahead of American Virginia Crawford in 12.59.
Steve Lewis finished fourth in the pole vault with 5.52m, with Frenchman Renaud Lavillenie winning with 5.77m.
Kenyan David Rudisha was half a second outside his own world record in the 800m but still set a new best time in the world this year in 1:41:54, obliterating the rest of the field.
Mo Farah, who has set the world-leading time of 12:56.98 in Eugene last month, was given a reminder of the task he faces to win 5,000m gold in London as Ethiopian Dejen Gebremeskel stormed to victory in 12:46.81 while his compatriot Hagos Gebrhiwet set a new world junior record of 12:47.53 in second, the duo dominating a high-class field featuring 10 Kenyans and five other Ethiopians including world record holder Kenenisa Bekele.