Wales turned in an inept display littered with horrendous defensive errors as they suffered their third heaviest defeat since 1930.
It was hoped that this generation of players could end a wait to reach a major finals that stretches back to 1958, but on the evidence of this shambolic display Wales are unlikely to be in Brazil in 2014.
Aleksandar Kolarov curled home a free-kick and Zoran Tosic doubled the home side's lead after some comedy defending had allowed Manchester City's Kolarov to slip past several challenges.
Gareth Bale got Wales back in it with a stunning free-kick but Darcy Blake's awful defensive header allowed Filip Djuricic to net Serbia's third before the break.
Dusan Tadic got the fourth before another gaffe from Blake let in Branislav Ivanovic and Miralem Sulejmani completed the rout.
Tuesday night's result leaves Wales rooted to the foot of Group A and Coleman admitted he was lost for words.
When asked to explain the defeat, he said: "Obviously I did not see it coming.
"We knew it would be difficult coming here but on the back of Friday's performance against Belgium we thought we could get something, but we can't accept that level of performance.
"To say it is disappointing is an understatement. We have to do much better than that and we are capable of doing much better.
"At times it was men against boys, the goals we conceded were criminal really and the individual errors were disappointing.
"To lose 6-1 is an absolute hammering and we can't ignore that, the manner of the performance was particularly disappointing.
"At this level you cannot gift teams goals, you have to at least be hard to beat and play with a bit of pride and we didn't do that. We caved in."
Chelsea won the Europa League on Wednesday. The Blues defeated Benfica 2-1 on injury time goal from Ivanovic.
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