Mo Farah's marathon debut proved a step too far as he trailed home in eighth place, outside the British record he had targeted, in London on Sunday.
The 31-year-old had made no secret this race was the toughest test of his career and he was never in contention, suffering in the last quarter of the race as the step up to 26.2 miles told.
Kenyan world record holder Wilson Kipsang took the Virgin Money London Marathon title in an unofficial time of two hours four minutes and 29 seconds, a course record, with Farah coming home almost four minutes back.
The Briton's time of 2hrs 08mins 21secs was outside Steve Jones' 29-year-old British record of 2:07:13 and could persuade him that his future remains on the track rather than the road.
Kenya's Stanley Biwott was second, with Ethiopian defending champion Tsegaye Kebede third.
The pain, though, was etched on double Olympic champion Farah's face over the final miles as he was cheered on to the finish.
He at least broke the English record held by Charlie Spedding at 2:08:33, but that was little consolation.
Farah admitted he was "disappointed" with his run and said it had been "pretty tough".
He was certainly up against an imposing field, which featured four of the 10 fastest marathon runners in history.
He was not helped by missing a drink stop shortly after the halfway mark. He was at that point running on his own, rather than in a group with others around to offer assistance with the pace.
The double London 2012 gold medallist insisted, though, he would persevere with the marathon and it had been the right choice to make his debut in the capital, despite the race offering a baptism of fire.
"I'm not going to finish it like this," he told BBC One straight after the race.
"I'll be back. It's a matter of experience and learning.
"It would have been disappointing to do my first marathon somewhere else.
"It's where I grew up. The crowd were absolutely amazing. I just wish I'd given a little bit more to the crowd and the supporters.
"This is my city. It would have been wrong to do any marathon. I had to do it (my first one) here.
"I gave it a go. That's all I could do. I'm just disappointed I didn't go out there and give a bit more what the crowd deserve and the people supporting me.
"But the field was tough. You've got Olympic champions just finishing now. It was the strongest field ever put together by the London Marathon.
"I've gone straight in at the deep end, but that's what athletics is all about."
But Brendan Foster, the commentator and former Olympic 10,000m bronze medallist, advised Farah to stick to what he knows.
He said: "I hope Mo stays on the track, runs the shorter distances and defends his (Olympic) title in Rio (in 2016). I just think this is too much of an unknown territory for Mo."
Farah's build-up to the race had hardly been ideal, collapsing after crossing the finish line in second at the New York City Half Marathon last month, although he insisted during the week he had suffered no ill-effects from that setback.
He received a huge cheer when introduced to the crowd at the start and certainly looked fired up, even kissing the badge on his new Great Britain kit.
He set off, as planned, with the second group, which dropped back quickly as the leaders opened at a crazy speed, well inside world record pace.
From 10 kilometres Farah started to claw back time, moving through the field and reducing the gap from 45 seconds to 38 seconds as he went through halfway in 1:03:08.
The missed drink stop and having to run on his own did not help his cause, but, even after he rejoined one of the pacemakers, he really started to struggle after the 25 kilometres mark.
He dropped 64 seconds off the leaders at 30km and more than two minutes off by 35km as he slipped outside British record pace, eventually coming home 3:52 behind Kipsang.
Farah added: "It was just the pace. It would have been nice to sit in a group.
"I wish I had gone with the front group. I had no-one to pace me because the pace-maker was slightly ahead."
But Jones sounded a more positive note, saying: "As a debut performance it was extremely good."
Chris Thompson, another debutant, was the second Briton home in an impressive 11th place, ahead of Olympic and world champion Stephen Kiprotich, in 2:11:19.
There was a Kenyan one-two in the women's race too, as Edna Kiplagat sprinted away from compatriot Florence Kiplagat down the Mall to win.
Kiplagat, the two-time reigning world champion, made up for the pain of finishing runner-up for the past two years in the capital to take the title in 2:20:21, with her namesake three seconds back.
Tirunesh Dibaba, the Ethiopian track great stepping up, like Farah, to 26.2 miles for the first time, had looked set to challenge the pair for much of the race, but paid the price for dropping a water bottle and having to stop to pick it up. She finished in third, 14 seconds adrift.
Amy Whitehead was the first Briton home in 13th.
Wheelchair racer David Weir's bid for a record seventh title ended in disappointment as Switzerland's Marcel Hug edged him out in a sprint finish.
The four-time London 2012 gold medallist did not quite have the strength to overhaul his rival in the closing metres as he finished one second adrift in second place.
American Tatyana McFadden successfully defended her women's crown, claiming a dominant victory just a month after winning a cross-country skiing silver medal at the Winter Paralympics in Sochi.
The 24-year-old crossed the line in a course record 1:45:12.