The 23-year-old Kenyan (pictured above), who won the world title in Daegu last year, produced the fastest 1500m time of the year, 3min 28.88sec, to finish ahead of fellow Kenyan Nixon Chepseba, who clocked a personal best of 3:29.77.

New Zealand's Nick Willis produced a national record of 3:30.35 in third place.

Kiprop's performance was matched by that of American Aries Merritt, who also produced a 2012 best to win the 110m hurdles in 12.93sec and will advance to London confident of his chances against a field that will include Cuba's world record holder Dayron Robles and China's 2004 Olympic champion Liu Xiang.

But there was a less happy experience for Merritt's cousin and compatriot, LaShawn Merritt.

The 2008 Olympic 400m champion, who will seek to defend his title 12 months after returning from a two-year doping suspension, suffered an injury scare as he pulled up after 200m of his race.

Aries Merritt of the United States pictured right

The American had almost caught 19-year-old Kirani James from Grenada, who beat him to the world title in Daegu last year, when he slowed and limped off the track.

But Merritt added later that his London defence was not in jeopardy as it was just a case of muscles tightening on a drab evening.

There was also disappointment for another Olympic champion, Russia's Yelena Isinbayeva, who failed to clear her first height of 4.70 metres in a pole vault competition won by Germany's Silke Spiegelburg, who cleared that height on a difficult day for vaulting.

Britain's Holly Bleasdale was third.

"I was a little bit surprised about my jumps," commented Isinbayeva.  

"All three were completely different – so I am not stable yet.

"But it is very important for me to defend my Olympic title in London."

In the 3,000m steeplechase, 17-year-old Conselus Kipruto defeated his hugely more experienced Kenyan compatriot Paul Koech, while in the women's 800m Burundi's African champion Francine Niyonsaba recorded her third consecutive national record, running 1:58.68 in finishing second to Russia's Yelena Kofanova, who recorded 1:58.41.

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