Triple Olympic champion Usain Bolt eased through to the second round of the 100m - but it was defending champion Tyson Gay who was the fastest qualifier.
Gay ran 10.16secs in winning his heat, with Britain's Dwain Chambers clocking 10.18 and Bolt 10.20. British number one Simeon Williamson and team-mate Tyrone Edgar also advanced by finishing second in their heats, in 10.34 and 10.42secs respectively.
Chambers said: 'I'm fully confident that I will run faster this afternoon.
'You can run fast in grand prix races, but this is a championship. Some people crack - I just have to make sure I don't.'
Earlier there was disappointment for Helen Clitheroe in the 3,000m steeplechase as she failed to qualify for the final after finishing ninth in her heat.
