The Olympic marathon champion has fallen agonising short in his bid to be the first athlete to run the distance in under two hours.
Eliud Kipchoge set an unofficial new world record as he came across the line at a Nike event at the Formula 1 grand prix race track Monza.
But the Kenyan runner's time of two hours and 25 seconds meant he narrowly missed out on his bold attempt to break the two-hour barrier.
The 32-year-old's time smashed the official mark of 2:02.57 set by fellow Kenyan Dennis Kimetto in Berlin in 2014.
But the run will not enter the record books largely due to a non-compliant system of pacemaking which saw runners come in and out of the attempt.
Kipchoge's run came 63 years to the day Sir Roger Bannister ran the world's first sub-four-minute mile.
Eritrea's Zersenay Tadese and Ethiopia's Lelisa Desisa also attempted the record in Italy but came home well off Kipchoge's blistering pace.
Despite it not being officially recognised, the Kenyan regarded his run as career defining, saying: "This is history."
The time comfortably beats his previous personal best of 2:03:05, which he set at the 2016 London Marathon.
He and the other two challenging runners missed this year's London and Berlin marathons to train to break the two-hour barrier.
Women's marathon world record holder Paula Radcliffe, who faces seeing her fastest run controversially erased, lauded Kipchoge's efforts.