Sonia O'Sullivan finished sixth in the Hydro Active Women's Challenge in London's Hyde Park.
The Cobh native, who is preparing for the Berlin Marathon later this month, surrendered her title while running a time of 17:34.
Derartu Tulu claimed victory after out-sprinting Susan Chepkemei in the final stages of the five kilometres race.
Ethiopia's double Olympic 10,000m champion piled on the pressure in the final 400 metres and crossed the line in 15 minutes 30 seconds, five seconds ahead of her Kenyan rival.
New Zealand's Kim Smith, recent winner of the World University Games 5,000m title, was third in 15min 50secs, more than 30 seconds ahead of first Briton Julia Bleasdale.
The winning time was some way slower than Paula Radcliffe's 2003 world record of 14min 51sec which she shares with Tulu's cousin Tirunesh Dibaba, but the Ethiopian was not complaining.
"I'm very happy with the time as I haven't trained since the World Championships," said Tulu, who finished fourth in the Helsinki marathon last month.
"I'm even more pleased to win because I've been finishing second and third a lot recently."
The leading two ran shoulder to shoulder up the final climb but it was Tulu who had more in reserve and she pulled away down the slope towards the finish line.
"I was confident coming to the finish," said the 33 year-old.
"I didn't think Susan would be a threat in the sprint and I felt good."
