That took almost two seconds off the time of 12:37.35 that has stood since 2004 to Etihiopia’s multiple world and Olympic champion Kenenisa Bekele.

It was the high point of a stupendous night of action in the Stade Louis II, a virtual solo run, with the nearest challenger being Nicholas Kimeli of Kenya, who clocked a personal best of 12:51.78 on a newly-laid track that replaced one which had produced legions of middle and longer distance flourishes down the years.

That tradition looks like being upheld in years to come.

Cheptegei, an ebullient and highly intelligent character, had spent lockdown training quietly back home, but when he arrived in the Principality he was happy to announce that he had the world record in mind.

Job done.

"I think Monaco is a special place," Cheptegei said.

"It took a lot of mind setting to keep being motivated this year. 

"I pushed myself, I had the right staff with me, the right coach. 

"I'm usually based in Europe, but being based in Uganda with my family was actually great."

Earlier in what turned out to be an epic programme, Kenya’s world 1500m champion Timothy Cheruiyot had won an almighty struggle with Norway’s 19-year-old European champion Jakob Ingebrigtsen, edging clear by 0.23 seconds in 3:28.45.

That was just short of Cheruiyot’s best of 3:28.41, set in the same stadium two years ago, which established him seventh on the all-time list.

Ingebrigtsen - finishing clear of Britain’s Jake Wightman, who clocked a personal best of 3:29.47 - was rewarded  with a European record of 3:28.68 that shifted him into eighth place on that all-time list -– massive consolation for failing to complete what would have been an outstanding Norwegian double on the night.

Earlier in the evening Norway’s double world 400m hurdles champion Karsten Warholm, who set a world 300m hurdles best on home territory at the Impossible Games in June, produced another bravura display as he won in a super-fast 47.10sec.

That was close to his personal best of 46.92, the second fastest ever recorded, and more than enough to hold off the challenge of Turkey’s Yasmani Copello, who clocked 49.04 in second place.

Warholm, who opened up a two-second lead with a stupendous late burst over the final two hurdles – unusually for his normal eyeballs-out racing plan -  had Kevin Young’s 1992 Olympics world record of 46.78 in mind, but ended up with  a 2020 world best and meeting record.

It was his second best performance of all time and his seventh sub 47.50 – a total only the great 1976 and 1984 Olympic champion Ed Moses of the United States has bettered.

Kenya’s world 5,000m champion Hellen Obiri produced a winning time of 14:22.12, the fastest run in the world this year and a meeting record.

Ethiopia’s Letesenbet Gidey, the world 10,000m silver medallist, was second in 14:26.27, with third place going to Britain’s Laura Weightman with a huge personal best of 14:35.44 that moved her to second on the UK all-time list.

Fourth place went to Australia’s Jessica Hull in a national record of 14:43.80, while Obiri’s compatriot Beatrice Chepkoech, the world 3,000m steeplechase world champion and world record holder was sixth.

The penultimate event, the women’s 1000m, produced another record-breaking performance with Kenya’s Rio 2016 1500m champion Faith Kipyegon setting a new African record of 2:29.15, ahead of Britain’s Laura Muir, who set a national record of 2:30.82.

That race had been preceded by a men’s 200m won in a 2020 world-leading time of 19.76 by US world champion Noah Lyles.

Despite a stellar field, the men’s pole vault suffered an early letdown as the double world champion Sam Kendricks, of the United States, was unable to start as his poles had not managed to make the journey with him.

That improved the odds for Sweden’s world record holder Armand "Mondo" Duplantis to get his Diamond League season off to a winning start.

Duplantis had also had a struggle getting his poles to the stadium, as there were limited flights available from his Swedish base to Monaco.

Having failed to find a flight that could take the poles, he had to rely upon another means of transport – a car driven by, as he described them, "three angels" - his mother and coach Helena, her sister and another friend, who completed a 25-hour road trip to deliver the tools of his trade.

Duplantis, who set successive world records of 6.17 metres and 6.18m in February before the coronavirus pandemic began to impact sporting competition, entered with a first-time clearance of 5.60m, a height that had already proved too much for Brazil’s Olympic champion, Thiago Braz.

The 20-year-old European champion eventually made his angels’ mercy drive worthwhile as he won with a first-time clearance of 5.80m.

But first he had to deal with an unexpectedly competitive challenge from Belgium’s Ben Broeders, whose first-time clearance of 5.70m had him under pressure after he had twice failed at the same height.

Duplantis, as so often before, found the way to progress with his third and final attempt, and neither Broeders, nor Ernest John Obiena of the Philippines, last year’s Asian Championships gold medallist, who cleared 5.70m at the third attempt.

Duplantis went on to clear 6.00m at the third attempt before failing with three attempts at 6.15m, which would have been an outdoor world record.

The 110m hurdles had got the meeting off to an electric start - a race in which the world champion, Grant Holloway of the United States, could only manage fourth place, in 13.19.

Victory went to Spain’s Rio 2016 silver medallist Orlando Ortega in 13.11 - displacing the man who finished second, Andy Pozzi - at the top of this year’s world list.

But the Briton, who ran 13.17 in Turku on Tuesday (August 11), could feel well pleased with his outing as he clocked a personal best of 13.14, with France’s Wilhem Belocian third in 13.18.

The men’s 800m went, as expected, to the US world champion Donavan Brazier, in 1:43.15, bettering his own 2020 world lead of 1:43.84.

All five runners behind Brazier ran personal bests, with fellow American Bryce Hoppel in 1:43.23 and Marco Arop of Canada third in 1:44.14.

In the women’s high jump, Ukraine’s 18-year-old world silver medallist from last year, Yaroslava Mahuchikh, cleared 1.98m to win on countback from her 22-year-old compatriot Yuliya Levchenko, the 2017 world silver medallist.

All the athletes were tested before the meeting for Covid-19 - a process which led to the world and Olympic 3,000m steeplechase champion Conseslus Kipruto having to remain in Kenya after a positive result.

In his absence, the concluding steeplechase went to Morocco's world bronze and silver medallist Soufiane El Bakkali in a 2020 world-lead of 8:08.04.

Because the normal call room is too small for social-distancing guidelines, the athletes had gathered instead on the stadium's infield before their events.

The Herculis meeting in Monaco usually features a capacity crowd of 16,000 but this was reduced to the maximum authorised number of 5,000 this year as part of the health and safety protocols in during the coronavirus pandemic.

Masks were obligatory for spectators in the Stade Louis II, hydro-alcoholic gel was widely available and in the grandstand every other row and every other seat was left free in order to ensure suitable social distancing.

Meanwhile, the World Athletics’ event presentation team introduced crowd atmosphere technology of the kind that is currently being used with football matches being played behind closed doors.