Farah, who claimed 10,000m gold on the opening day of the 15th International Association of Athletics Federations' (IAAF) World Championships here, has been beleaguered this summer by allegations of doping abuse, levelled at his coach Alberto Salazar rather than him personally.

The 32-year-old British double reigning Olympic champion pulled out of the IAAF Diamond League meeting in Birmingham in June and flew back to his training base in Oregon, claiming he was “emotionally exhausted” by the controversy.

But his return to racing last month demonstrated he had not allowed those circumstances to affect his running, and he proved it again in the Beijing 2008 Ollympic stadium as he retained his title in 27min 01.13sec.

“It means so much,” said Farah after he had outsprinted a Kenyan trio of Geoffrey Kamworor, second in 27:01.76, Paul Tanui, who took bronze in 27:02.83, and Bedan Muchiri to take a fourth world title, having taken the lead shortly before the bell.

 “It hasn’t been an easy year, but at the same time it is nice to get the team started well.

“I just get to keep on doing what I’m good at and that is running and winning medals for my country - I just have to concentrate on winning my races.

“I do it for my family and the people behind me, for my wife and my kids.

“My wife is expecting soon, another baby is on the way.”

On an opening day of action in which Usain Bolt, who clocked 9.96sec, was given a first-hand glimpse of what it will take to defend his 100m title against Justin Gatlin of the United States - who ran a first round time of 9.83sec on the newly-laid, super-fast Mondo track - Farah’s was the last of three golds to be won.

Others went to 19-year-old Ghirmay Ghebreslassie of Eritrea, who became the youngest man to win the men’s world marathon title, and to Germany’s Christina Schwanitz, who survived an inspired challenge from home thrower Lijiao Gong to earn victory in the women’s shot put.

A huge opening effort of 20.30 from Gong put her into a first round lead that she maintained until Schwanitz’s third round effort of 20.37 generated a huge murmur of dismay.

Gong’s responded with 20.25, but could do no more, ending up with a third medal in five World Championships for the Chinese athlete, after bronze in 2009 and 2013.

“It is my first silver medal, but it is still a shame, because I got very close to becoming champion,” she said.

Schwanitz added: “Gong was very concentrated  and very tense, but mentally she is not as strong as me yet.”

Ghebreslassie took a decisive lead after after 35km of the marathon - by which point the immediate past and current world record holders, respectively Wilson Kipsang and Dennis Kimetto, had dropped out in conditions of high heat and humidity.

Even before the 7.35am start, it had been 22C with humidity of 73 per cent, before it got hotter.

The young man seemed overwhelmed by what he had accomplished, maintaining: “My parents wanted me to be a great student, but I wanted to be a great athlete."

Earlier in the day the Championships were declared open here in by Chinese President Xi Jinping.

In his preceding address, Lamine Diack, who will hand over his position as IAAF President to Sebastian Coe with his sport beset by media criticism over doping issues, said: “Seven years ago we witnessed an Olympic Games here and the world wondered at an exceptional track and field meeting in which five world records were set.

"The eyes of the sporting world are here again on Beijing.

“As I prepare to stand down at the end of these Championships it therefore gives me great personal pleasure to witness China hosting the IAAF’s top event as well as the last Congress of my Presidency.

“We look forward to nine days of fierce competition in a spirit of honesty, integrity and fair play.”

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August 2015: Bubka to miss whole World Athletics Championships due to family illness
July 2015: Mo Farah cleared of any wrongdoing by UK Athletics over links with coach Salazar
July 2015: Farah questioned by USADA lawyer amid doping allegations against coach Salazar
July 2015: Farah dedicates Lausanne Diamond League win on competitive return to coach Salazar