AFC Wimbledon produced a stunning performance to hold off a second-half comeback from West Ham and earn a 4-2 FA Cup scalp.
The side bottom of League 1 turned the form book on its head and showed more industry and desire than their Premier League visitors in the first half, and were rewarded with a comfortable lead at the break through Kwesi Appiah's deflected opener (34) and Scott Wagstaff's smart finish on the break (41).
West Ham looked far more competitive following a triple half-time substitution from Manuel Pellegrini, but not before Wagstaff had scored Wimbledon's third just 37 seconds after the restart when his superb flick from Appiah's cross beat Adrian.
The Hammers threatened to extinguish hopes of an upset through two of those substitutes, with Lucas Perez firing in from a corner (57) and Felipe Anderson scoring direct from a free-kick (71).
But Wimbledon did not let their increasing pressure tell and wrapped up a famous victory when 19-year-old Toby Sibbick nodded in Anthony Wordsworth's cross with two minutes remaining, sending the sell-out home crowd into pandemonium.
Pellegrini made six changes from last week's defeat at Bournemouth but the Hammers' side still had Premier League experience from back to front, although in the opening 45 minutes it was difficult to believe they were the top-flight side in the tie.
Wimbledon worked the ball forward with quality and pace and although West Ham hit the post through a deflected Javier Hernandez effort, it was one of few half-chances they fashioned before the break.
Instead, Wimbledon took the lead with a slice of good fortune their play had thoroughly deserved when Appiah's shot from 20 yards took a big deflection off Angelo Ogbonna to wrong-foot Adrian.
Their second, seven minutes later, summed up their performance when Appiah robbed Pedro Obiang in midfield, with Wagstaff picking up the loose ball and he raced beyond the West Ham defence to slot inside the near post.
Pellegrini threw on Anderson, Perez and Ryan Fredericks at the break but their first job was to watch Wagstaff volley in Appiah's measured cross from the left with a brilliant flick into the far corner.
From then on, the visitors had the lion's share of possession and play but with a three-goal handicap, had it all to do. But they certainly smelt an opportunity once Perez fired home powerfully once Michail Antonio's shot had been saved by Aaron Ramsdale.
The Hammers kept on knocking and Anderson curled in a second from a 25-yard free-kick following a clumsy challenge from Will Nightingale, but Wimbledon held firm and denied them any further clear-cut chances.
They gave them a lesson in creativity when the hosts resisted the temptation to pull men back once a late corner had been cleared, allowing Wordsworth to pick out substitute Sibbick, who nodded in his first goal in more than a year from close-range, sparking scenes of wild celebration in the stands well before the full-time whistle with a spot in the fifth round assured.
Opta facts
- AFC Wimbledon have won all four of their FA Cup matches this season to progress to the fifth round for the first time since their reformation in 2002.
- West Ham have been eliminated from the FA Cup by a League One side for a second consecutive campaign (Wigan in 2017-18, AFC Wimbledon today); it is the first time they have been knocked out of the competition by sides from a lower division in back-to-back tournaments since 1998-99 (Swansea City) and 1999-00 (Tranmere Rovers).
- West Ham have conceded four goals in a single FA Cup game against a side from the third tier or below for the first time since January 1936 when they lost 4-0 to Luton Town in a third round replay.
- AFC Wimbledon scored more than one goal in a single match in the FA Cup proper against a side from a higher division than themselves for the very first time in what was their 10th such contest since their reformation in 2002.
- Today was just the second time that AFC Wimbledon have progressed from an FA Cup proper tie against a side from a higher division, and the first since they beat Scunthorpe United in a first round replay in 2011-12.
- AFC Wimbledon's Kwesi Appiah has been directly involved in six goals in his last six appearances in the FA Cup proper (four goals, two assist), including four in two this season (two goals, two assists).
- Kwesi Appiah has had a hand in five goals in his last three games for AFC Wimbledon (three goals, two assists) in all competitions, as many as his first 26 appearances of this season combined before today.
- AFC Wimbledon's Scott Wagstaff scored his first ever brace in professional football; he had scored just two goals in his last 44 appearances in all competitions before today.
- No Premier League player has scored more goals as a substitute in all competitions this season than West Ham's Lucas Pérez (4 - level with Pierre-Emerick Aubameyang).
- Felipe Anderson is the first player to score a direct free-kick in the FA Cup for West Ham United since Dimitri Payet against Manchester United in March 2016, 1049 days ago.
Man of the match - Dylan Connolly
Going on this performance the buy of little-known Connolly from Irish side Dundalk looks a stroke of genius. On his first start since his January 3 arrival, he made three key passes, as many as anyone else on his side, and his crossing deserved more from his forward team-mates.
He won 78.6 per cent of his 14 duels on the night - a higher proportion than any other Wimbledon player - and gave Arthur Masuaku a torrid time on the right until he was withdrawn exhausted with four minutes left.
What's next?
Wimbledon face another tough test when they travel to promotion-chasing Sunderland in League 1 next Saturday at 3pm. West Ham are back in action on Tuesday night, when they visit Molineux to face Wolves at 7.45pm.