Tyson Gay was disappointed with his performance after winning the 200 metres in a meeting record 19.72 seconds at the Monaco Diamond League event on Thursday.
The 27-year-old was ahead off the bend and poised for a comfortable victory until Jamaican Yohan Blake, running in lane eight, came blazing down the home straight and almost closed the gap on the tiring American.
"I ran too wide in the corner, I slipped a bit. I wanted to run faster but it's okay," Gay, the 2007 world champion, said.
Blake, training partner of world record holder Usain Bolt, clocked 19.78 to improve his personal best by almost a second.
On a hot and humid evening that produced seven world leading efforts, there was also frustration for 110 metres hurdler David Oliver, who had targeted Dayron Robles' world record of 12.87 but hit two barriers on his way to the line in 13.01.
"My reaction wasn't really good. I wasn't ready. I wasn't completely set," said Oliver, who ran 12.89 in Paris last week.
"That's okay, I have got the stadium record and points in the Diamond League. I want to win the Diamond League this year."
Kenyan Silas Kiplagat pipped Moroccan Amine Laalou on the line in the men's 1,500 to post a year's best time of 3:29.27 and lower his personal best by five seconds.
"I knew I could do it. I could not say I ran to do it but I bettered my personal record. That's very important," said the 20-year-old Kiplagat.
Jamaican Jermaine Gonzales won the 400 metres in a world leading 44.40, beating the mark of 44.49 set by former world and Olympic champion Jeremy Wariner last week in Paris,
Triple world long jump champion Dwight Phillips posted 8.46 metres on his first attempt to improve the year's best he set in Rome last month.
Russian Ivan Ukhov confirmed he would be a favourite for the high jump title at next week's European championships in Barcelona by clearing 2.34 at his first attempt.
Cuban world champion Yargelis Savigne recorded the longest triple jump of the season with 15.09.
A strong piece of front-running gave American Alysia Johnson victory in the 800 in a world leading 1:57.34. There was also a year's best time for Ethiopian Sentayehu Ejigu in the 3,000 in 8:28.41.