05/20/2012 03:29 EDT | Updated 07/20/2012 05:12 EDT

2 months before London Olympics, British race organizers put out wrong number of hurdles

MANCHESTER, England - Running on home soil nearly two months before the London Olympics, Jessica Ennis thought she had produced a career best in the 100 metres hurdles — until organizers discovered a major blunder.

Only nine hurdles had been set out instead of the regulation 10 at the Great City Games in Manchester, northern England on Sunday.

Ennis described it as a "massive, massive mess-up."

The Briton had clocked 12.75 seconds into a headwind to beat Olympic champion Dawn Harper and world silver medallist Danielle Carruthers.

In a statement organizers said: "We would like to apologize for this unacceptable incident."

They blamed UK Athletics, who are employed "to manage this vital element of the event on our behalf, and we will of course be investigating this unfortunate occurrence with them."