Mauro Boselli scored twice to help Wigan fight back and defeat fellow Premier League side West Ham in the Capital One Cup third round.
James McArthur's error let Modibo Maiga power in a shot for the Hammers.
Wigan responded with Boselli converting a Callum McManaman cross and Ivan Ramis scoring with a 20-yard strike.
Boselli lifted the ball over keeper Stephen Henderson for his second and Jordi Gomez scored from the spot to seal the win.
The defeat is West Ham's first at home this season and came after both sides made plenty of changes from last weekend's Premier League matches.
Hammers boss Sam Allardyce made nine changes to his side, while counterpart Roberto Martinez made seven.
Maiga was one of those to come in for the home side and he quickly made his presence felt.
McArthur was caught in possession by the Mali international, who fired into the bottom corner past keeper Ali Al-Habsi.
Boselli's cup of cheer
Mauro Boselli has yet to score in the Premier League since arriving at Wigan in 2010. The Argentinian striker, who has spent half a season on loan at Genoa and a year back at former club Estudiantes, has scored all four of his Wigan goals in the League Cup.
Wigan gradually improved, with David Jones having a shot saved by Stephen Henderson and Boselli heading wide.
Boselli has struggled since a £6m move to Wigan from Estudiantes in June 2010 but played a pivotal role in helping his side through to the last 16.
The Argentine, 27, lost his marker to get on the end of a Maynor Figueroa cross and poke the ball past Henderson for an equaliser.
West Ham allowed their visitors too much time and space and that was epitomised when Ramis scored his first Wigan goal.
The Latics centre-back ran on goal from the halfway line before finishing it off with a long range shot.
Boselli extended his side's lead with a lovely chip over Henderson as West Ham struggled to match their rivals.
The home side rarely looked like mounting a comeback and were put out of their misery when Gomez scored from the spot after Henderson had hauled down McArthur.
West Ham manager Sam Allardyce: "We couldn't defend a fish supper tonight. There were howling errors from our defenders in all four goals, it was comical.
"I never expected us to defend so poorly. It was really poor defending and all the good work we might have done with the ball meant nothing in the end because out of possession we were just rubbish.
"It was an embarrassing defeat. They can't come knocking on my door about not playing now. They've got to take responsibility for their performance. They should have given me a lot more value for my money than they did."
Wigan manager Roberto Martinez: "We're happy with how it went given there were changes. It was a real test of character, especially from the young lads.
"To score four goals away is a real achievement, especially at West Ham with the way they have started the season.
"He [Mauro Boselli] showed mental strength and how focused he is to be a success this season and to enjoy his football. If he is at his best he will be a real asset for us."
West Ham United
- 13 Henderson
- 03 McCartney
- 05 Tomkins
- 27 Spence
- 33 Potts
- 07 Jarvis
- 16 Noble (Taylor - 72' )
- 32 O'Neil (Tombides - 84' )
- 11 Maiga
- 12 Vaz Te (Fanimo - 62' )
- 46 Hall
- 30 Spiegel
- 19 Collins
- 41 Driver
- 14 Taylor
- 39 Tombides
- 40 Fanimo
- 45 McCallum
- 26 Al Habsi
- 05 Caldwell Booked
- 21 Ramis
- 23 Stam
- 24 Lopez
- 31 Figueroa
- 06 Jones
- 16 McArthur (Fyvie - 85' )
- 15 McManaman (Gomez - 74' )
- 19 Boselli (Orsula - 90' )
- 32 Miyaichi
- 12 Pollitt
- 17 Boyce
- 08 Watson
- 14 Gomez
- 20 Fyvie
- 02 Kone
- 35 Orsula
Live Text Commentary
Full Time The referee blows for the end of the match.90:00 +2:57
The ball is sent over by Ronnie Stam, James Tomkins manages to make a clearance. David Jones takes a shot from inside the box clearing the bar.90:00 +2:22
The official flags Modibo Maiga offside. Adrian Lopez takes the indirect free kick.89:35 Substitution
Substitution Filip Orsula is brought on as a substitute for Mauro Boselli.86:40
Short corner taken by Jordi Gomez.86:08
Free kick awarded for a foul by Modibo Maiga on David Jones. Maynor Figueroa restarts play with the free kick.84:48 Substitution
Substitution James McArthur leaves the field to be replaced by Fraser Fyvie.83:43
The assist for the goal came from James McArthur.83:43 Goal scored
Goal! - Jordi Gomez - West Ham 1 - 4 Wigan Placed penalty scored by Jordi Gomez. West Ham 1-4 Wigan.80:49 Substitution
Substitution Dylan Tombides joins the action as a substitute, replacing Gary O'Neil.80:49
Penalty awarded for an unfair challenge on James McArthur by Stephen Henderson.78:50
Outswinging corner taken from the left by-line by Matthew Taylor, clearance by Ryo Miyaichi.78:36
Robert Hall takes a shot. Save made by Ali Al Habsi.78:16
The ball is crossed by Ryo Miyaichi.77:26
Mauro Boselli takes a shot. Comfortable save by Stephen Henderson.77:05
The ball is sent over by Matthew Taylor, Gary Caldwell makes a clearance.76:29
The ball is swung over by Daniel Potts, save by Ali Al Habsi.75:46
The ball is crossed by Ryo Miyaichi, Mauro Boselli takes a shot. The assistant referee flags for offside against Ryo Miyaichi. Stephen Henderson restarts play with the free kick.73:11 Substitution
Substitution Callum McManaman leaves the field to be replaced by Jordi Gomez.73:11
A cross is delivered by Matthias Fanimo.
The ball is swung over by Daniel Potts, clearance by Ivan Ramis. Inswinging corner taken from the left by-line by Matthew Taylor, save made by Ali Al Habsi.71:29 Substitution
Substitution Mark Noble goes off and Matthew Taylor comes on.70:57
Matthew Jarvis sends in a cross, Gary Caldwell manages to make a clearance.69:49
Daniel Potts challenges Ryo Miyaichi unfairly and gives away a free kick. Free kick taken by Ivan Ramis.69:02
David Jones gives away a free kick for an unfair challenge on Mark Noble. Mark Noble takes the direct free kick.68:47
The ball is crossed by Gary O'Neil, clearance made by Gary Caldwell.67:25
Robert Hall crosses the ball, clearance made by Adrian Lopez.66:58
Inswinging corner taken by Robert Hall from the right by-line, clearance by Adrian Lopez.66:44
James Tomkins takes a shot. Adrian Lopez gets a block in.65:57
Adrian Lopez concedes a free kick for a foul on Modibo Maiga. Mark Noble restarts play with the free kick.65:03
David Jones decides to take a short corner.64:39
The ball is delivered by Robert Hall, James Tomkins takes a shot. Comfortable save by Ali Al Habsi.63:56
Maynor Figueroa concedes a free kick for a foul on Matthias Fanimo. Free kick taken by Mark Noble.62:08
Unfair challenge on Callum McManaman by Gary O'Neil results in a free kick. Gary Caldwell restarts play with the free kick. David Jones takes a shot. Blocked by James Tomkins.61:25 Substitution
Substitution Ricardo Vaz Te goes off and Matthias Fanimo comes on.59:33
Centre by Jordan Spence, Header on goal by Modibo Maiga from inside the box goes harmlessly over the target.55:55
Free kick awarded for an unfair challenge on Ryo Miyaichi by Daniel Potts. Ivan Ramis takes the direct free kick.55:42
The ball is sent over by Jordan Spence, blocked by Adrian Lopez.54:29
Ricardo Vaz Te produces a right-footed shot from outside the penalty box and misses left.52:11
The ball is delivered by Matthew Jarvis, clearance made by Ivan Ramis.51:44
Gary O'Neil crosses the ball, clearance made by Ryo Miyaichi.49:05
Foul by James Tomkins on Callum McManaman, free kick awarded. Gary Caldwell restarts play with the free kick.46:50
The referee blows for offside against Callum McManaman. Free kick taken by Stephen Henderson.45:01
The referee starts the second half.45:00 +3:02 Half time
Half Time The referee calls an end to the first half.44:24
Mark Noble takes the free kick. Shot by Robert Hall from outside the box goes high over the crossbar.44:24 Booking
Booking Booking for Gary Caldwell for unsporting behaviour.44:06
Gary Caldwell concedes a free kick for a foul on Robert Hall.43:54
Centre by Jordan Spence, Adrian Lopez manages to make a clearance.40:10
James McArthur provided the assist for the goal.40:10 Goal scored
Goal! - Mauro Boselli - West Ham 1 - 3 Wigan Mauro Boselli scores a goal from inside the penalty box low into the middle of the goal. West Ham 1-3 Wigan.37:23
The assist for the goal came from Ryo Miyaichi.37:23 Goal scored
Goal! - Ivan Ramis - West Ham 1 - 2 Wigan Ivan Ramis finds the back of the net with a fantastic goal from outside the area to the bottom left corner of the goal. West Ham 1-2 Wigan.34:48
George McCartney sends in a cross, Header from deep inside the area by Robert Hall goes harmlessly over the crossbar.34:16
The ball is sent over by Modibo Maiga.31:17
Shot by Ricardo Vaz Te from 30 yards. Ivan Ramis gets a block in. Mark Noble takes the inswinging corner, Ali Al Habsi makes a comfortable save.28:49
Maynor Figueroa fouled by Ricardo Vaz Te, the ref awards a free kick. Ali Al Habsi restarts play with the free kick.27:26
Jordan Spence has an effort at goal. Save made by Ali Al Habsi. Corner from the right by-line taken by Gary O'Neil, Close range headed effort by James Tomkins goes wide of the left-hand upright.26:39
The ball is crossed by Mark Noble, clearance made by Ivan Ramis.26:18
Mark Noble decides to take a short corner.25:52
The ball is crossed by Ronnie Stam, Stephen Henderson makes a comfortable save.22:47
The ball is swung over by Matthew Jarvis, clearance made by Ivan Ramis. The ball is sent over by Gary O'Neil, save made by Ali Al Habsi.21:17
The ball is sent over by Jordan Spence, Maynor Figueroa gets a block in.20:11
Robert Hall has an effort at goal from long range that goes wide left.19:24
Effort on goal by Maynor Figueroa from inside the penalty box misses to the right of the target.17:20
Mark Noble fouled by Ronnie Stam, the ref awards a free kick. Stephen Henderson restarts play with the free kick.15:31
The ball is crossed by James Tomkins, comfortable save by Ali Al Habsi.13:48
Assist by Maynor Figueroa.13:48 Goal scored
Goal! - Mauro Boselli - West Ham 1 - 1 Wigan Mauro Boselli gets on the score sheet with a goal from close range to the bottom right corner of the goal. West Ham 1-1 Wigan.12:52
Free kick awarded for an unfair challenge on Ryo Miyaichi by George McCartney. David Jones has an effort direct from the free kick, save by Stephen Henderson.11:49
Ricardo Vaz Te crosses the ball, Gary Caldwell makes a clearance.10:56
The ball is swung over by Maynor Figueroa, Headed effort from inside the area by Mauro Boselli misses to the left of the goal.10:29
James Tomkins takes a shot. Save by Ali Al Habsi.9:56
Gary Caldwell gives away a free kick for an unfair challenge on Robert Hall. Direct free kick taken by Mark Noble.6:20 Goal scored
Goal! - Modibo Maiga - West Ham 1 - 0 Wigan Modibo Maiga fires in a goal from just inside the penalty area to the bottom left corner of the goal. West Ham 1-0 Wigan.4:05
Corner taken short by David Jones. Effort from outside the penalty box by Ryo Miyaichi goes wide right of the goal.3:20
Jordan Spence delivers the ball, Header on goal by James Tomkins from inside the box goes harmlessly over the target.2:52
Mark Noble takes the inswinging corner, clearance by Gary Caldwell.0:00
The match has kicked off.
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