Once again, yet again, Jamaican super sprinter Usain Bolt has come to the rescue of track and field.

With American Justin Gatlin the hottest of favourites in the 100m at the world championships in Beijing, the sport was bracing itself for a public relations nightmare.

Gatlin has served two doping bans, with incoming IAAF president Sebastian Coe just one of many who dreaded how a victory by him in athletics’ most prestigious event would have been perceived.

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He needn’t have worried.

Bolt – who first rose to global prominence with his triple gold medal haul at the 2008 Beijing Olympics – powered home on Sunday night to win his third world 100m title in 9.79 seconds.

Gatlin tightened up late in the race and was second in 9.80, while American Travyon Bromell and Canadian Andre de Grasse tied for bronze with 9.92.

It was Gatlin’s first defeat this year.

As recently as last month, it was doubtful whether Bolt would even make it to the start-line in Beijing as he battled to overcome a leg injury.

Two runs of 9.87 in London convinced the Jamaican he was ready, but Gatlin was still the short-priced favourite, even more so after dominating the heats and semi-finals.

Bolt has won every 100m and 200m Olympic and world title he has contested since 2008 – except for the 100m world crown in 2011 when he false-started in the final.

Gatlin, 33, served his first doping ban in 2001 after testing positive to a banned substance in ADHD medication.

He returned to win gold at the 2004 Athens Olympics before again testing positive, this time to testosterone.

That offence would have normally have carried a life ban, but was cut to eight years, and then four, after Gatlin agreed to co-operate with anti-doping authorities.

Jessica Ennis-Hill after winning gold in the heptathlon. Photo: AAP

In other action on Sunday, Britain’s Jessica Ennis-Hill made a triumphant return to top-level competition only 13 months after the birth of her son Reggie by winning gold in the heptathlon.

Ennis-Hill, the 2012 London Olympic champion, iced the victory with a powerful victory in the concluding 800m and finished with a total of 6669 points.

The minor medals went to Canada’s Brianne Theisen-Eaton and Laura Ikauniece from Latvia.

American Joe Kovacs won the men’s shot put with 21.93m, ahead of German David Storl and Jamaica’s O’Dayne Richards.

New Zealander Tommy Walsh smashed his own Oceania record with 21.58m in the fifth round, but it was only good enough to net him fourth place.

The other gold medals decided on day two of the championships went to Poland’s Pawel Fajdek in the men’s hammer throw and Miguel Angel Lopez from Spain the men’s 20km walk.

-AAP