West Ham have been dumped out of the FA Cup at the hands of League One, while in-form Arthur Masuaku was sent off for an spitting incident.
The Latics' hero was the Northern Ireland international striker Will Grigg, who again found himself the subject of the home fans' favourite chorus of "Will Grigg's On Fire" as he headed home after seven minutes and converted a second-half penalty.
To compound their misery, the Hammers, who also suffered injuries, had to play for more than 40 minutes with 10 men after Masuaku was sent off soon after the break for spitting at Wigan's Nick Powell.
Having made six changes to his side for the visit to the third-tier leaders, Moyes must have recognised the worst once he saw Grigg send a powerful header past England goalkeeper Joe Hart as Wigan dominated the early stages.
Wigan's fortunes have dipped since lifting the Cup in 2013, the year they also earned the unwanted distinction of being the only side ever to win the trophy while also being relegated from the top flight.
Yet their fans at the DW Stadium, who have recently been used to their side upsetting Premier League sides in the FA Cup, were left in ecstasy when Grigg scored his second in the 62nd minute from the spot after a hand-ball from Reece Burke.
