Lord Coe admitted he was far from "eulogistic" to see twice-banned American sprinter Justin Gatlin win the 100 metres at the World Championships in London.
Coe, president of the International Association of Athletics Federations (IAAF), conceded it was "not the perfect script" for Gatlin to triumph on what many hoped would be Usain Bolt's night.
In Bolt's final individual race before retirement, the 11-time world champion could only take third place, behind US sprinters Gatlin and Christian Coleman.
"Sport rarely settles upon the perfect script. Life's just not like that," Coe said.
"It's not the worst result ever. I'm hardly going to sit here and tell you I'm eulogistic that somebody that has served two bans in our sport would walk off with one of our glittering prizes, but he is eligible to be here."
Coe said that as head of the IAAF he would have to congratulate Gatlin if their paths crossed in London.
"I think the journey to that point is not a comfortable one for me." He added: "It's not the perfect script."
Gatlin, who returned from his second suspension in 2010 after four years out of the sport, has found himself cast as the pantomime villain in his battle with Bolt.
He was roundly booed once the crowd in London's 2012 Olympic stadium realised Gatlin had crossed the line first on Saturday night.
Coe stressed the IAAF tried to effectively end Gatlin's career following his second failed drugs test in 2006.
"There have been two bans in the past, one which got watered down which made it very difficult for the second ban," Coe said.
"The second ban we went for an eight-year ban which would have in essence been a life ban - we lost that. So these things are suffused in legality."