BERLIN: The meeting every athletics fan wished for became reality on Sunday as both triple Olympic champion Usain Bolt and triple world champion Tyson Gay reached the 100 metres final here at the world championships.

Bolt - also a triple world recordholder - false-started for the first time in his career before running a scintillating 9.89sec to win his semi-final.

Gay, who had a miserable Olympics failing even to reach the final, showed considerable resilience in reeling in Bolt's Jamaican team-mate Asafa Powell and ground out a workmanlike victory in 9.93sec.

Great Britain's Dwain Chambers completed his return to the summit of sprinting, after serving a two-year doping ban, by qualifying in fourth in Gay's semi-final.

"That's the first time I've false started," said the 22-year-old Bolt. "See you later, because I've got a long way to walk (to the warm-up track)."

Kenya's women's 800m world champion Janeth Jepkosgei suffered a rollercoaster day of emotions.

The 26-year-old is bidding to retain her title and restamp her authority on the event after her protege 19-year-old Pamela Jelimo trounced her in the Olympic final last year - fine reward for the older woman advising her to move up to that distance.

However, Jepkosgei tumbled on the final bend of her heat while leading when she became entangled with teenage South African Caster Semenya and finished a forlorn last while the South African recovered her composure to win.

The Kenyans, though, lodged a successful appeal and Jepkosgei was reinstated to run in Monday's semi-finals.

Ironically Semenya's participation is far from certain as a result of the entanglement.

"At the moment I have no feeling in my ankle. I need to see the physio to check my leg. If it's not good I'll quit," said the 18-year-old.

The only final of the morning session saw Russia capture their second walk title in as many days as defending world and Olympic champion Olga Kaniskina won the women's 20 kilometres walk world title by almost a minute.

The 24-year-old beat home Ireland's Olive Loughnane while China's Hong Liu took the bronze to make up for her upset at being fourth in last year's Olympics in front of her home supporters.

"This was not a very tough competition for me because I have already experienced harder races," said Kaniskina, who received a two bedroom apartment from the government of the Russian Republic of Mordovia when she won the title in 2007.