Emil Jaaskelainen scored the only goal of the game as Blackpool shocked West Ham United in the FA Youth Cup.
West Ham had the better of the opening period of play, with Rosaire Longelo looking threatening down the right-hand side, before Blackpool got a foothold in the game.
The left wing was the main source of danger for the visitors, with both Rowan Roache and Nathan Shaw getting down that side and getting balls into the box.
The second time Nathan Shaw got free down the left side, his ball in nearly fell for Will Dunne, but the striker couldn't quite get the right touch on the ball.
The hosts then came back into the game with another good spell. Both Rosaire Longelo and Domingos Quina had chances, but both efforts went wide.
Craig Thordarson was then called into action, with the Blackpool ‘keeper diving down to his left to make a sharp save, before watching a harmless free-kick fly over his crossbar.
West Ham had another couple of free-kicks on the edge of the box, but could not find a breakthrough from either as the first-half came to a close.
Half-Time: West Ham United 0 Blackpool 0
Once again, The Hammers came out strong to start the second-half, with Longelo firing straight at Thordarson in the opening minute.
Reece Hannam’s ball in from the left almost caused a problem for Thordarson, but he was able to change direction, after the ball was deflected, to save.
Blackpool then had the best chance of the game, as Owen Watkinson saw his effort from inside the box magnificently blocked by a West Ham defender. Will Dunne’s shot from the edge suffered the same fate moments later.
Halfway through the second stanza, Emil Jaaskelainen came on for Will Dunne as The Seasiders looked to take the game to the hosts.
Just eight minutes later, the substitute gave Blackpool the lead. Watkinson made the goal, after winning the ball down the left, before driving past the defender and squaring the ball for Jaaskelainen, who calmly slotted home.
West Ham were then awarded a penalty, after Nathan Shaw handled the ball in the box. However, Thordarson dived low to his left to save the penalty and preserve Blackpool’s lead.
The visitors then made their second change, with Tom Williams coming on for Harry Winstanley at the back, hoping to hold on for the final six minutes.
There was then a chance to double the lead, as Blackpool were awarded a penalty after Watkinson was bundled over in the box. However, Rowan Roache hit the bar with the spot-kick, leaving the score at 1-0.
The first minute of five added on saw West Ham down to ten men. Alfie Lewis was dismissed for head-butting Jaaskelainen.
Lewis Wainwright came on for Owen Watkinson in a defensive change for the final few minutes of the game, and the visitors held on for a huge victory.
Full-Time: West Ham United 0 Blackpool 1
Team: Thordarson; Jacobson (c), Avon, Winstanley (Williams 84’); Adarkwa, Newton, Sumner, Shaw; Roache; Watkinson (Wainwright 90’), Dunne (Jaaskelainen 67’)
Unused Subs: Simson, Flynn