Hicham El Guerrouj's 29-race unbeaten streak in the 1500m came to an end at Friday's Golden Gala meeting in Rome when he finished eighth.
With six weeks to go until the Olympics, El Guerrouj came in more than two seconds behind surprise winner Rashid Ramzi of Bahrain.
Ramzi set a new Asian record of 3:30.25 in winning the men's 1500m ahead of Kenya's Bernard Lagat.
El Guerrouj had not lost since coming in second at the 2000 Sydney Olympics.
But the gap between him and his rivals had been slimming during the past three 1500m, which he won by margins of just 0.03, 0.04 and 0.05 seconds.
Friday's defeat came on the same track where he set the world record of 3:26.00 in 1998, which still stands.
Britain's Michael East was seventh in a new personal best of 3:32.37.
Slovenia's Jolanda Ceplak ran the fastest women's 800m in 2004 so far.
The 2002 European champion held off the challenge by Russia's Svetlana Cherkasova to cross the line in one minute 57.68 seconds.
Her time beat the previous season's best set by Olympic champion Maria Mutola by 0.04 seconds.
Her feat was matched in the men's 800m by world record holder Wilson Kipketer, who ran 1:43.88.
In the men's 100m, Ghana's Zakari Aziz
won in 10,10 ahead of Jamaica's Thomas Dwight, with Britain's Darren Campbell setting a season's best of 10.21 in finishing fifth.
Campbell also set a season's best in the men's 200m, with his 20.59 enough for sixth in a race won impressively by Stephane Buckland.
"I'm the only one who ran in both the 100m and then the 200m 45 minutes later," he said.
"I've got to be pleased with what I've achieved, particularly in the 200 where I ran 20.59secs, my fastest time this season.
"It proves I've got lots of strength and, more importantly, I'm injury-free."
American Allen Johnson edged out China's Xiang Liu in a photo finish to a high quality men's 110m hurdles, in which both runners were clocked at 13.11.
Tonique Williams-Darling of the Bahamas came out on top in the women's 400m, winning in a world-leading 49.25, ahead of Mexico's Ana Guevara.
Chris Rawlinson was unable to end Felix Sanchez's awesome three-year unbeaten run in the men's 400m hurdles.
Sanchez won in 48.43 seconds, with Rawlinson just edged out by France's Naman Keita in the race for second place.