World record holder Kipchoge dropped from lead group in last 4km as 2019 runner-up Kitata takes victory on special looped course in St James's Park.
Eliud Kipchoge suffered only his second defeat in 11 marathons as Shura Kitata claimed his first London Marathon victory on Sunday (4 October).
The reigning Olympic champion was in a lead group of eight men inside the last 5km having looked slightly ill at ease.
And when Kitata pressed the pace at the front, Kipchoge was unable to respond and soon lost touch.
The Ethiopian continued to force the issue, and he out-sprinted Vincent Kipchumba to win in 2:05:41.
On a special loop course in St James's Park closed to the public, the wet and chilly conditions put paid to any attempt at Kipchoge's own world record of 2:01:39 from Berlin in 2018.
A slow pace made it a tactical battle, and it was Kitata who emerged victorious in a thrilling race.
Kipchoge eventually finished eighth in 2:06:49.
2020 Getty Images
Kitata wins tactical battle to go one better than 2019
After a calf injury ruled out three-time Olympic track champion Kenenisa Bekele on Friday, Kipchoge was fully expected to maintain his seven-year unbeaten marathon record.
The pace was leisurely by his standards with the field running the first half-marathon in just under 63 minutes.
At 30km, Kipchoge was lying seventh in a group of nine runners and not looking completely at ease.
He then threw away his cap and made his way ominously to the front alongside fellow Kenyans Benson Kipruto and Vincent Kipchumba.
Last year's runner-up Shura Kitata then moved to the head of affairs with Kipchoge content to sit in the middle of the group.
But as Kitata upped the pace, Kipchoge cracked with his unbeaten record stretching back to September 2013 coming to an end.
2020 Getty Images
Kosgei retains women's title
Earlier, Brigid Kosgei made it back-to-back London Marathon wins with USA's Sara Hall taking a surprise second place.
Kosgei had reigning world champion Ruth Chepngetich for company most of the way before pulling clear at the 30km mark.
The 26-year-old won in 2:18:58, almost five minutes outside her world record set in Chicago last year.
Hall charged home to overhaul Chepngetich inside the last 100m and take second in a new personal best of 2:22:01.
Kosgei said of her decisive move, "I didn’t have anything planned, but I felt good. I felt my body wanted to move, but my legs could not move, so I tried my best."
"The weather affected us today – there was some wind and rain all the way, which made our muscles colder. No one could warm up so it was difficult to even finish."
By Olympic Channel