MONACO (AFP) — Jamaica's Nickel Ashmeade won the 200 metres at Diamond League event here yesterday.

The Jamaican clocked 20.02, to beat Dutchman Churandy Martina (20.07) and Wallace Spearmon (20.09).

Meanwhile, the United States athletes experienced highs and lows marked by an injury scare for LaShawn Merritt, but world-leading times for hurdler Aries Merritt and the men's 4x100m relay team.

LaShawn Merritt, the favourite for 400m gold at the London Games, pulled up holding his left thigh after 300 metres of his race, although he insisted that his premature withdrawal was purely a precaution.

Belgium's Jonathan Borlee was a surprise winner in 44.74 seconds, ahead of Grenada's Kirani James (44.76sec).

Disaster struck for the women's top 4x100m relay team, who were unable to finish their race after a mix-up during the final baton hand-over.

The 'Red' team, featuring Tiana Madison, Allyson Felix, Jeneba Tarmoh and Carmelita Jeter, had established a healthy lead but Tarmoh and Jeter were unable to transfer the baton at the last change-over.

The USA's second-string relay squad, known as the 'Blue' team, nonetheless won the race, with Lauryn Williams, Alexandria Anderson, English Gardner and Kimberlyn Duncan coming home first in a time of 42.24sec.

There was much better news in the men's race, where Trell Kimmons, Justin Gatlin, Tyson Gay and Ryan Bailey romped to victory in 37.61sec — the fastest time in the world this year.

Aries Merritt ran a world-leading time of 12.93sec in the 110m hurdles for the third time this year to confirm his credentials as a serious contender for the gold medal in London.

There were also year's best marks for Kenya's world and Olympic champion Asbel Kiprop in the men's 1500m (3min 28.88sec) and Germany's Silke Spiegelburg in the pole vault (4.82m).

Russian pole vault queen Yelena Isinbayeva endured a dismal night as she failed with three attempts to clear 4.70m, gifting victory to Spiegelburg and raising serious questions about her chances at the London Olympics.

Nigeria's Blessing Okagbare triumphed in the women's 100m in a personal best time of 10.96sec, while Kenyan Conselus Kipruto celebrated a memorable victory in the 3,000m steeplechase (8min 03.49sec) at the age of just 17 years and 225 days.

The ninth leg of the Diamond League circuit was the last major meet before the Olympics begin on July 27.