Jamaican sprint king Usain Bolt (C) competes to win the Men's 100 metres during the first day of the London Grand Prix at the Crystal Palace Stadium on Friday.Photo: AFP

Sprint superstar Usain Bolt won the 100m at the London Grand Prix here on Friday in astounding style on a day when it was announced five of his fellow Jamaicans had tested positive for drugs.
Despite running into a stiff head wind, world record-holder Bolt, the Olympic 100m and 200m champion, still clocked a time of 9.91sec even though he clearly slowed down in the closing stages.
Bolt, who in Beijing last year set a world record of 9.69sec while winning gold, was not the quickest away from the start but once he was into his stride no-one in final at the Crystal Palace track in south London ever looked like catching him.
It was a display to worry rivals ahead of next month's World Championships in Berlin but Bolt, who finished second in his heat, told the BBC afterwards: "I am ready for anything that comes my way. I am not invincible, I am not unbeatable. Other people will have a good day when I don't, but until then I'll keep winning."
Reflecting on the race, he added: "Overall the main aim for me was the first 50m and I did well, I got it right so I'm happy.
"I knew it was going to be a headwind so I wasn't worried about the time. I got a good start, the transition was good so I'm happy with myself.
"I'm still at 85 per cent and after this it's all training, I've got two or three weeks of good training to put in so I guess I will be 100 per cent by Berlin," he added.
Fellow Jamaican Yohan Blake was a distant second to Bolt in 10.11 secs with Antigua's Daniel Bailey third.
Jamaica's former world record-holder Asafa Powell, who before this race insisted Bolt could be beaten, finished well down the field in sixth place.
In the women's pole vault Russia's Yelena Isinbayeva suffered her first defeat in a major event since the 2003 World Athletics finals.
World record holder Isinbayeva was beaten on countback by Anna Rogowska of Poland after only clearing 4.68m, the height at which she entered the competition, at her third and final attempt.
Mo Farah failed to break the 27-year-old British record for 5,000m but did at least win the race in a time of 13 minutes 09.14 seconds.
Dave Moorcroft's mark of 13mins 00.41secs - a world record at the time - has stood since July 1982 and Farah, running into a headwind, was always going to be struggling to go under that time.
"It was pretty windy but I just wanted to win if I couldn't run a time and I'm really happy with it," Farah said.
Britain's Nicola Sanders, a silver medallist behind compatriot Christine Ohuruogu in the last World Championships in Osaka, continued her return from an ankle injury to win the women's 400m ahead of the American duo of Shana Cox and Monica Hargrove.
"I was exhausted coming into the home straight but I'm pleased with the win," Sanders said.
Olympic silver medallist Phillips Idowu could only finish third in the triple jump, with America's Brandon Roulhac winning and Cuba's David Giralt in second place.
Earlier Friday, the International Association of Athletics Federations (IAAF) confirmed that five Jamaican sprinters - four men and one woman - had tested positive for a banned substance at the country's world championship trials.
The five do not include Bolt or Powell or any of the country's top sprint stars.