World 400metres champion Christine Ohuruogu expects winning Olympic gold will be a much tougher challenge than her comeback success at Osaka last summer.

Ohuruogu opened her one-lap campaign for 2008 with victory at the Golden Spike meeting in Ostrava, clocking the fastest time by a European athlete this year in the process.

The 24-year-old Commonwealth champion won in 51.06sec, finishing ahead of American Ebonie Floyd and Russia's Tatyana Veshkurova.

However, with American Olympic favourite Sanya Richards already getting into great shape, Ohuruogu predicted she will have smash Kathy Cook's 24-year-old UK record of 49.43sec if she is to win in Beijing.

"It is going to be very hard to defend the position of world No1 at the Olympics," said Ohuruogu.

"But I want to try it. It will be necessary to run sub 49 seconds to get gold.

"It was my first outdoor 400m this year so I am satisfied with my time." she added after yesterday's race.

Martyn Rooney maintained his position at the head of the European 400m rankings but failed to improve on his personal best of 45.19sec though Tim Benjamin had a night to forget in his season's opener, finishing eighth in 47.94sec.

Fellow Britons Michael Rimmer and Mo Farah also failed to make an impression. Rimmer finished ninth in the 800m and 17th in the 5,000m respectively.

Cuba's Dayron Robles set a new world record of 12.87sec in the 110m hurdles, slicing one-hundreth of a second off the previous mark.