Richards must still win in Berlin and Brussels for a Golden League prize

Richards set the fastest time in the world this year, clocking 49.36 seconds with the Briton back in fourth.

Richards, 22, missed out on the 400m in Osaka after failing to qualify for the USA team in the event.

The win saw the 2005 world silver medallist stay on track for a share of the IAAF $1m Golden League jackpot.

Ohoruogu, on her Golden League debut, looked jaded from her efforts in Japan and finished in 51.32sec.

Richards admitted she was determined to put on a good show after missing out in Osaka

606: DEBATE No team can match the USA in track and field at the moment but some individuals might knock them off the top spot. GBsupporter

"I expected a fast race because I wanted to attack my personal best. Entering the final straight, I didn't know they were so far behind," she said.

"It was mentally tough for me but I was ready to pull out a great victory. It was my world championships here."

There were two other jackpot contenders after three meetings in the series.

Russia's Olympic and world champion Yelena Isinbayeva stayed on course for a share of the top prize after she dramatically won her pole vault competition with her final attempt of 4metres 80cm, beating compatriot Svetlana Feofanova into second.

But two-time world champion Michelle Perry lost her chance of sharing in the pot when she suffered a shock defeat in the 100m hurdles.

The American was beaten by Sweden's European champion Susanna Kallur and Ennis-London Delloreen, of Jamaica, into third place in a time of 12.68 seconds.

Isinbayeva soars over to keep her Golden League hopes alive in Zurich

Elsewhere, American sprinter Xavier Carter marked his return from a leg injury, sustained during the US trials prior to Osaka, with victory in the 200m.

Francis Obikwelu of Portugal won a depleted 100m race in 10.17sec, after double world champion Tyson Gay and 100m silver medalist Derrick Atkins withdrew from the race, both citing tiredness.

Britain's Marlon Devonish was second in 10.20sec, level with Jaysuma Saidy Ndure, of Norway.

French athletes started the evening by winning the first two major races after Osaka, where they failed to win a single event.

Two-time European champion Mehdi Baala won the 1500m immediately before Christine Arron triumphed in the women's 100m.

Arron led from start to finish to win in 11.17 ahead of American Torri Edwards (11.22), with Carmelita Jeter third in 11.24. Lauryn Williams, the 2005 world champion who lost a photo finish to Jamaica's Veronica Campbell in Osaka, was only seventh.

Xavier Carter, who failed to qualify for Osaka because of injury sustained at the US trials in June, won the 200m in 19.92sec, beating world silver medalist Usain Bolt (20.19) into second.