Striker Ashton celebrates his last-gasp winner at Upton Park
Dean Ashton smashed home on the volley in stoppage time to snatch a dramatic victory for West Ham to see them into the fourth round of the Carling Cup.
It was cruel luck on Plymouth, who had fought hard throughout and brought much frustration from the home supporters.
Sylvan Ebanks-Blake had a shot blocked for Argyle, while Lucas Neill cleared Barry Hayles' effort off the line.
The hosts had chances too, Luis Boa Morte firing wide and James Collins going close, before Ashton's fine goal.
It ensured the Hammers continue in a competition Alan Curbishley has publicly targeted a trophy from.
But Plymouth will be cursing their luck after a valiant effort that almost got off to a fine start when Danny Gabbidon's back-pass dropped short with Ebanks-Blake bearing down on goal, stand-in goalkeeper Richard Wright doing well to clear.
The Hammers should have been ahead minutes later, Peter Halmosi clearing Collins's header off the line and Ashton turning and firing narrowly wide from 20 yards.
It was left to Boa Morte to miss the chance of the half, though, the winger playing a one-two with Hayden Mullins only to clip wide when through.
With the home fans increasingly unsettled, Argyle grew in confidence and Neill had to be alert to chest Halmosi's free-kick away late in the first half.
And, after Carlton Cole's exit had been roundly cheered by the Hammers fans - the striker had earlier dallied when clear on goal - Ebanks-Blake almost snatched the lead for Plymouth only for George McCartney to block well.
There was still time for the striker to see another fine shot brilliantly cleared off the line by Neill, while Lee Bowyer headed wide from three yards at the other end.
But, with the match seemingly destined for extra-time, Ashton popped up with a brilliant volley to snatch the win.
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