Steve Morison fired League One Millwall into the fifth round of the FA Cup with a 1-0 upset win over Premier League Watford at the Den on Sunday.
The Lions knocked Bournemouth out in the previous round and added another top-flight scalp to their collection, with top scorer Morison volleying home substitute Shane Ferguson's cross with five minutes remaining to win the tie.
Watford, who made seven changes for the game, had two penalty appeals turned away but Walter Mazzarri's side can have few complaints at the final whistle after struggling to create clear-cut openings against a team 41 places below them in the football pyramid.
Millwall could have been ahead inside the first 30 seconds. Morison was sent clear down the right channel and his cross was volleyed onto the bar by his strike partner Lee Gregory.
That fast start from the hosts continued with left-back Tony Craig seeing his long-range shot from distance deflected narrowly over the bar for a corner but Watford hit the woodwork themselves on 25 minutes when Millwall defender Shaun Cummings flicked Adlene Guedioura's free-kick onto the far post.
The Hornets had struggled to get out of their own half in the early stages but 10 minutes later they were appealing for a penalty when Jerome Sinclair miscued his shot from 15 yards out. The forward was under pressure from Millwall's Shaun Williams but appeared to kick the ground rather than be fouled.
There was then immediate confusion up the other end of the pitch as a poor back pass from Miguel Britos allowed Gregory to slide in on Costel Pantilimon. Fortunately for Watford, Adrian Mariappa was on hand to relieve the danger but Pantilimon was forced off with an ankle injury from Gregory's challenge.
Substitute Heurelho Gomes was soon called in action, pulling off a fine save to parry Gregory's close-range volley around the post for a corner before Guedioura headed Morison's goal-bound effort from the resulting set-piece clear.
Millwall started the second half in rapid fashion, too, and Gregory really should have found the net from Morison's knockdown a minute after the break but instead blazed over.
Watford had a second penalty appeal turned away on 53 minutes when Stefano Okaka appeared to be hauled down by Byron Webster as he tried to meet Guedioura's cross.
The Premier League side dominated possession in the second period but Morison tested Gomes with a hooked shot with 10 minutes to play and Millwall then had a penalty shout of their own when Ferguson's cross hit Brandon Mason.
But moments later the home team was celebrating when Morison met Ferguson's angled pass and drilled the ball in off Gomes for his 14th goal of the season.
Webster then seemed to have doubled Millwall's lead when he bundled in a cross a minute later but his effort was rightly ruled out for handball.
Watford threw everyone forward in search of an equaliser but Webster's last-ditch block denied substitute Troy Deeney from close range before a scramble in the box from the resulting corner eventually led to a goal-kick.
Millwall then saw out the final moments to reach the fifth round of the FA Cup.