Mutai smashed the course record with a dominating performance that left the defending champion Tsegaye Kebede floundering in his wake, while Keitany won the women's race in a time only world record holder Paula Radcliffe has ever beaten on the London course.
A year ago, Mutai made a late surge to finish second, but this time he left little to chance, bursting away after 20 miles and powering home in the last six mile to win in 2:04:40, half a minute quicker than Sammy Wanjiru's record from 2009, making Mutai the fourth fastest man in history.
"Since I've come to run in London I have twice finished fourth and last year I was second," said the 26-year-old who also picked up a silver at the World Championships and was second in New York last November.
"This year I have come back and my dreams have come true. I so much wanted to win a major marathon and this time I did it."
Keitany also made a dramatic burst to leave defending champion Shobukhova and a clutch of highly talented rivals in her wake. The world half marathon record holder strode home alone in 2:19:19 to move alongside Irina Mikitenko as the equal fourth fastest woman in history.
After smashing the world half marathon record earlier this year, Keitany has announced herself on the marathon stage in superb style, improving her lifetime best by nearly 10 minutes.
Behind the winners, three-times London winner Martin Lel made a remarkable return to marathon running to take second in the men's race in a sprint finish ahead of 2010 Berlin champion Patrick Makau.
Both recorded 2:05:45, a time only 30 seconds outside his Lel's personal best. It was an astonishing performance from the former champion as he was only added to the entries three weeks ago and hasn't run a marathon since the 2008 Beijing Olympics.
As for Kebede, he had to be satisfied with fifth in 2:07:48 after Mutai ground his dreams of a world record into the London dust.
Shobukhova rallied in the final stages of the women's race to take second in 2:20:15, while Edna Kiplagat added a place on the London podium to the New York title she won last year, taking third in 2:20:46.
David Weir made history in the wheelchair races, becoming the first man ever to win five men's titles.
The Briton powered home in 1:30:05 ahead of Swiss world record holder Heinz Frei, while American Amanda McGrory outsprinted Shelly Woods to regain the women's title she won two years ago in 1:46:31.
London Marathon 2011- Top 10 Results
- Mutai, Emmanuel (KEN) 02:04:40
- Lel, Martin (KEN) 02:05:45
- Makau, Patrick (KEN) 02:05:45
- Dos Santos, Marlison Gomes (BRA) 02:06:34
- Kebede, Tsegaye (ETH) 02:07:48
- Gharib, Jaouad (MAR) 02:08:26
- Bouramdane, Abderrahime (MAR) 02:08:42
- Safronov, Dmitry (RUS) 02:09:35
- Bat-Ochir, Serod (MGL) 02:11:35
- Shelley, Mike (AUS) 02:11:38
- Keitany, Mary (KEN) 02:19:19
- Shobukhova, Liliya (RUS) 02:20:15
- Kiplagat, Edna (KEN) 02:20:46
- Bekele, Bezunesh (ETH) 02:23:42
- Baysa, Atsede (ETH) 02:23:50
- Akaba, Yukiko (JPN) 02:24:09
- Mikitenko, Irina (GER) 02:24:24
- Augusto, Jessica (POR) 02:24:33
- Kebede, Aberu (ETH) 02:24:34
- Konovalova, Mariya (RUS) 02:25:18
[Virgin London Marathon]