The equation had seemed simple enough for Arsenal. Take a home victory from a team towards the foot of the table and stride decisively towards an automatic Champions League berth. Yet nothing has been entirely simple for them. Indeed, the unpredictability of matches in England this season has reached glorious new heights.

Here was another helter-skelter example and the latest twist in Arsenal's impossible-to-script campaign. Wigan Athletic not only stormed into an early two-goal lead but they held their hosts at arm's length with remarkable comfort in the second half, when they even looked the likelier scorers. In Victor Moses they had the game's outstanding performer and the winger's only blot was his inability to finish when clean through in the 60th minute.

Hard on the heels of their victories over Liverpool and Manchester United this was a stunning coup for Wigan. It is now four wins in five for Roberto Martínez's team and the one that got away was the defeat at Chelsea, when they were wronged by the officials. In this form and with these levels of confidence it is outlandish to imagine them in next season's Championship. Martínez brimmed with pride and satisfaction. Wigan had previously tasted only defeat at Arsenal.

The emotions, though, were rather different inside his opposite number. Arsène Wenger bubbled with anger throughout the game at the time-wasting tactics of the Wigan goalkeeper Ali Al-Habsi, which began when he dragged his heels over a goal-kick in the third minute. When Al-Habsi was finally booked in injury-time, for pushing the gamesmanship too far, Wenger raged at the fourth official, Kevin Friend. The unpalatable truth, though, was that Arsenal could have played for another 45 minutes and not threatened. The second half for them did not feel so much like a bad day at the office as one for the P45s.

There was rancour at full-time, when Wenger stalked off down the tunnel. Gary Caldwell, the Wigan captain, went to shake Robin van Persie's hand only to be rebuffed. There was a brief kerfuffle and players from both sides had to step in. It looked like something and nothing. Arsenal had to be more concerned at their failure to open up an eight-point lead over Tottenham Hotspur in fourth. Their addiction to taking matters to the wire continues. Does anybody want to make sure of third?

The defeat was costly yet the stakes were arguably higher for Wigan: the retention of Premier League status means everything to them, in sporting and financial terms. Martínez's men had arrived in their finest form of the season yet the start that they made was simply staggering. The tiny enclave of travelling supporters were buzzing with delight from Franco Di Santo's opening goal, converted after a well-constructed and incisive counter-attack, when Moses flummoxed Bacary Sagna and crossed low from the left. James McArthur attacked the ball and, when it broke, Jordi Gómez beat Wojciech Szczesny at the second attempt.

Wenger was unhappy that his team had only 10 men on the field at the time, Mikel Arteta having limped off with a worrying-looking ankle injury and, because there was no stoppage in play, the Frenchman was unable to get Aaron Ramsey on.

Martínez's formation, with its unorthodox lack of symmetry, was designed to provide defensive strength and pace on the break, and he could revel in Di Santo's goal, which stemmed from an Arsenal corner. James McCarthy, Moses and Gómez were instrumental in the move and Di Santo fashioned the finish, getting the ball over the advancing Szczesny and running on to volley home.

Arsenal's response to this double hit was initially ferocious. Yossi Benayoun had forced Al-Habsi to tip over a smart header in the fifth minute and he made him save again, acrobatically, with another header. There was an inevitability about Arsenal reducing the deficit and Thomas Vermaelen seemed to dispatch Tomas Rosicky's whipped cross with a snarl. Van Persie stung Al-Habsi's palms from distance; Johan Djourou volleyed inches wide and Rosicky scooped over.

Yet Arsenal were slipshod and nervous in defence and after the interval they ran out of steam and ideas. Al-Habsi was not required to make a save and Martínez said the second half was as well as Wigan had played all season. The reward was wonderfully sweet.