Usain Bolt up Against Justin Gatlin in 100m Sprint at World Athletics

Usain Bolt bids to retain his title as the world's fastest man on day two of the world athletics championships on Sunday.

The Jamaican easily qualified for the 100 metres semifinal along with American rival Justin Gatlin, who set the fastest qualifying time of 9.83sec.

As Bolt goes mano a mano against Gatlin, the muscle men go for glory in the shot put and hammer, with an absorbing women's heptathlon also reaching its conclusion.

But all eyes will be on Jamaican superstar Bolt, who faces a serious challenge from American Gatlin in a blockbuster clash in Beijing, where Bolt famously blasted to triple gold at the 2008 Olympics.

"I was just trying to execute and save as much energy as possible," Bolt said after winning his heat. "I'm in wonderful shape."

Gatlin, 33, who has twice failed doping tests in the past, has clocked this season's fastest time of 9.74 seconds, while world record holder Bolt returned from injury with a 9.87 in London last month.

Such has been the towering Jamaican's complete dominance of sprinting since 2008 that astonishingly time he failed to land a major title was when he was disqualified for a false start in the 100m in Daegu four years ago.

Bolt's eye-popping world record of 9.58, set in Berlin in 2009, would appear safe but with allegations of widespread doping engulfing the sport, his showdown with Gatlin is being seen by some as a symbolic struggle of light versus dark.

In the men's shot put, Germany's David Storl will be aiming for a hat-trick of world titles, although American champion Joe Kovacs looks a formidable obstacle having heaved a season-best 22.56 metres in Monaco recently.

Barring a major upset, the gold medal will be contested by Storl and Kovacs, the only two men registering throws of beyond 22 metres this year with three Diamond League wins apiece.

Poland's hulking hammer king Pawel Fajdek looks a solid bet to retain the title he won in Moscow, coming into the championships on the back of 15 successive victories and monster throw of 83.93 metres -- 10th on the all-time list.

Hungarian Olympic and European champion Krisztian Pars is likely to be Fajdek's main contender but he has failed to throw over 80 metres and may need to produce something special if he wants to improve on than the silver medals he won in 2011 and 2013.

Olympic champion Jessica Ennis-Hill produced a dazzling first-day display in her quest for a second world heptathlon title by storming into the lead after the opening four events.

Making her return to major competition with some panache after giving birth last year and a battle with niggling injuries, Ennis-Hill will carry an 80-point lead over fellow Briton Katarina Johnson-Thompson into Sunday's final three events.

"I didn't expect to be leading at this stage," said the Briton.

"I don't think I did anything particularly amazing, but was just able to hold my form through all four events. I'll be very satisfied if I can do that tomorrow."

Saturday begins, however, with an early morning start in the men's 20km walk to protect athletes from Beijing's air pollution while there will also be heats in the men's 400 and 800 metres.

Jamaica's double Olympic champion Shelly-Ann Fraser-Pryce begins her quest to win an unprecedented third women's 100m world title in Saturday's morning heats.