Like the sub-four minute mile, running a marathon in less than two hours had seemed impossible — until Saturday. But this time there's an asterisk: Olympic champion Kipchoge performed his feat under conditions so tightly controlled to maximize his success that it won't appear in the record books.

The 34-year-old Kenyan completed the 42.195 kilometers (26.2 miles) in 1 hour, 59 minutes, 40.2 seconds at the INEOS 1:59 Challenge, an event set up for the attempt.

Ahead of the event, Kipchoge even compared the feat to being "like the first man on the moon." Afterward, he drew comparisons to Bannister, the late Briton who 65 years ago became the first athlete to run a mile in under four minutes.

"It is a great feeling to make history in sport after Sir Roger Bannister," Kipchoge said. "I am the happiest man in the world to be the first human to run under two hours and I can tell people that no human is limited. I expect more people all over the world to run under two hours after today."

With all variables tailored to his advantage, it was still the full marathon distance but it was no regular marathon race, which means his jaw-dropping finishing time will not be ratified by IAAF.

Different to an ordinary race, event organizers had set a nine-day window to be flexible and stage the run in the best possible weather conditions.

Also, Kipchoge was supported throughout his run by 36 pacemakers who accompanied him in alternating groups, with five athletes running ahead of him in a V-shape and two others closely following.

Unlike a normal race, a timing car just in front of the pack also helped keep the scheduled pace, and was equipped with a laser beam, projecting the ideal position on the road, parts of which also had painted stripes to indicate the optimum running line.

Furthermore, Kipchoge received drinks handed over by a cyclist to prevent him from having to slow down.

Even though his attempt was never meant to set an official world record, Kipchoge was understandably delighted and twice punched his chest in celebration while smiling when he finished.

"That was the best moment of my life," he said, before adding that he trained 4 ½ months for his extraordinary race against the clock. "The pressure was very big on my shoulders. I got a phone call from the president of Kenya."

In a statement, President Uhuru Kenyatta said: "Hearty congratulations, Eliud Kipchoge. You've done it, you've made history and made Kenya proud. Your win today will inspire future generations to dream big and aspire to greatness."

Kipchoge said his mission went beyond athletics.

"We can make this world a beautiful world and a peaceful world," he said. "The positivity of sport. I want to make it a clean sport and an interesting sport."

Kipchoge was cheered by thousands along the course in Prater Park and there were celebrations in his home country before he had even finished.

Hundreds of joyous Kenyans brought traffic to a standstill in the middle of the capital, Nairobi, as they gathered to watch the end of the run on a large screen. People pumped their fists, clapped and fell to their knees as Kipchoge cruised to the finish line.

In Kenya's running mecca of Eldoret, called the home of champions, hundreds of people burst on to the streets in celebration.

"We should line up the entire road from the airport to Nairobi. Receive him like the hero he is," prominent activist Boniface Mwangi said on Twitter.

Running at an average pace of 2 minutes, 50 seconds per kilometer (around 4:33 per mile), Kipchoge was 11 seconds ahead of schedule halfway through his run. He then maintained his tempo until the pacemakers left him for the final 500 meters, where he sped up.

"I was really calm, I was just trying to maintain the pace," said Kipchoge, adding he was never in doubt about breaking the barrier. "For me it was not 50-50, it was 90%."

Jim Ratcliffe, founder of the chemicals company backing the attempt, exchanged high-fives with Kipchoge after the finish.

"He even accelerated in the final kilometer, he is a superhuman," Ratcliffe said. "I can't believe he's done it. He did the first half in less than an hour and then he's just done that again."

Organizers said normal anti-doping regulations were in place and that Kipchoge and all the pacemakers were being tested in and out of competition by the Athletics Integrity Unit (AIU).

The team behind the event "has ensured all athletes involved in the project are undergoing extensive intelligence-led testing that has been pioneered by the partnership between Abbott World Marathon Majors and the AIU," they said in a statement to The Associated Press.

The Prater Park in the Austrian capital offered long straights, protected from the wind by high trees, for most of the 9.6-kilometer course, which Kipchoge completed more than 4 times.

It was his second attempt at breaking the two-hour barrier, after missing out by 26 seconds at a similar event on the Formula One track in Monza, Italy, in May 2017.

Kipchoge, who took Olympic gold in Rio de Janeiro in 2016 and has won 10 of his 11 marathons, holds the official world record of 2:01:39 since shattering the previous best mark by 78 seconds in Berlin last year.

In the near-perfect circumstances at the meticulously planned attempt, Kipchoge shaved almost two minutes off that time.

Long-time coach and mentor, Patrick Sang, a former Olympic and world steeplechase silver medalist, said it was "really exciting."

"I am happy for him and what he has achieved. He has inspired all of us that we can stretch our limits and that we can do more than we think we can do," Sang added.

Under Sang's guidance, Kipchoge won gold in the 5,000 meters at the world championship in 2003, the start of a distinguished track career which includes Olympic bronze and silver medals from 2004 and 2008.

After missing out on qualification for the 2012 London Olympics on the track, Kipchoge switched to the marathon and has since been pushing the boundaries of the discipline. But he still faces one big challenge — to run under two hours in a regular marathon race.