In-form Jason Roberts and Henri Camara did not have to be asked twice as they capitalised on the Hammers' defensive deficiencies to give Wigan a deserved fourth successive victory in this thoroughly one-sided match.
At the start of the season, the smart money was on newly-promoted Sunderland, West Ham and Wigan all returning from whence they came.
But while Mick McCarthy's rock-bottom Black Cats already appear ripe for relegation, Paul Jewell's Latics now occupy the heady heights of fifth with Alan Pardew's beaten Hammers nestling just four places below them.
Injury-hit West Ham made three changes following their Boxing Day draw at Portsmouth as Carl Fletcher, Christian Dailly and David Bellion each made rare starts.
Not surprisingly, Wigan were unchanged after their 4-3 win over Manchester City and Roberts - their two-goal hero at the JJB Stadium - should have opened the scoring in the 10th minute, but after out-muscling James Collins, he prodded wide with the whites of Roy Carroll's eyes in his sights.
And with the lively Latics starting brightly, the home keeper also found himself bravely diving at Camara's feet after his defence was again breached.
Apart from wayward shots by Hayden Mullins and Anton Ferdinand, plus a blocked Bellion effort, West Ham struggled to find a route to goal and that was the catalyst for shocked substitute striker Bobby Zamora to replace the frustrated Fletcher with only 25 minutes on the clock.
Still Wigan piled on the pressure and former Upton Park youngster Jimmy Bullard was the next to test Carroll with a thunderous, low 20-yarder that was beaten aside by the Northern Ireland international.
As the interval arrived, however, West Ham were flattened by that knockout blow of a weighty Wigan one-two that saw the eastenders floored by a quick-fire double.
First Roberts punished Ferdinand's poor 43rd-minute clearance by collecting Camara's return and juggling his way through the flat-footed home defence before looping the ball wide of the furious Carroll.
And just over 60 seconds later, Pardew's men were yet further behind as Camara slid home from eight yards after they again failed to deal with another incisive Latics raid into the heart of the West Ham defence.
Having failed to force visiting keeper Mike Pollitt into a single save, the trailing Hammers departed to a chorus of deserved boos and, facing a second half mountain of Everest proportions to climb, they made yet another switch at the break as Shaun Newton replaced Bellion.
Exactly a year ago to the day, Pollitt had been in goal for a relegation-bound Rotherham United as they squandered a two-goal lead against a West Ham side that bagged a brace of late penalties to force a 2-2 draw at Millmoor.
But 365 days on, there was to be a far happier ending for the Wigan keeper, for apart from seeing both Paul Konchesky and Mullins both have efforts charged down in quick succession, Pollitt and his team-mates were never in danger of leaving freezing Upton Park with anything less than a clean sheet and three richly deserved points