Ben Watson’s exocet header a minute into added time sent the 23,000 Latics fans into ecstasy as they watched their team not only win the Cup for the first time but also clinch the first major trophy in the north-west club’s 91-year history.Given the disparity in the resources of the two clubs, with City’s super-rich status in stark contrast to minnows Wigan, the achievement of Roberto Martinez’s team in overcoming the sky blues will go down as the biggest FA Cup shock since Wimbledon beat Liverpool in 1988.The outcome hinged upon two decisive moments late in what had been a generally flat match. In the 84th minute, City right-back Pablo Zabaleta was sent off after collecting a second yellow card for a wayward tackle on man-of-the-match Callum McManaman.Sensing this could be their opening, Wigan threw men forward and created a series of set-piece openings.With two of the three minutes of added time remaining, Shaun Maloney’s whipped-in corner from the right was met by substitute Watson, who wrote himself into Wigan folklore by rising above Jack Rodwell and powering an unstoppable header past Joe Hart to stun a rain-soaked Wembley.With the dark blue flags flying high in the grey north London sky, it was a memorable end to what had been a generally forgettable encounter.City had begun the match as strong favourites but this was a wretched display from the 2011 FA Cup champions.They were sluggish, ponderous and struggled to get out of first or second gear. Reports in Spain on Friday night claimed that Malaga manager Manuel Pellegrini has agreed a deal to take over as manager at the end of the season from Roberto Mancini.If, as appears increasingly likely, that proves to be the case then the Italian, whose competitive fire burned as strongly as ever in the technical area, will regard this as a dismal end to his three-and-a-half years in Manchester.More than a quarter of the 80,000 population of Wigan were present at Wembley Stadium for the greatest day in the club’s history but it did not reflect well on the FA’s ticketing policy that empty red seats were discernible in the Latics’ end.Perhaps this contributed to a strangely subdued first half atmosphere. There were intermittent bursts of noise from the Wigan fans but the City supporters, bar the early point they made about singing Mancini’s name lustily, were collectively flat.City began ominously, with Zabaleta threatening on the overlap and Argentine front pair Carlos Tevez and Sergio Aguero looking dangerous.But the sky blue pressure petered out and Wigan, who were beaten at home in a must-win match by Swansea City five days earlier, began to settle into a groove.McManaman carved open the City defence every time he twinkle-toed in from the wing, giving the run-around to Gael Clichy in particular.With Shaun Maloney’s sure touch and passing range helping Wigan to keep the ball, the underdogs were giving as good as they got.By contrast, City’s big guns were mis-firing. Aguero and Tevez became increasingly frustrated up front, David Silva and Samir Nasri flitted in and out of the game, while Yaya Toure played too deep to be a major attacking influence.Martinez got his tactics spot on, soaking up City possession, confounding them with an unorthodox 3-4-1-2 formation and using McManaman’s pace and trickery to stretch the favourites on the counterattack.When Zabaleta saw red late on, Wigan threw caution to the wind and went for the kill. With Watson making the decisive contribution 10 minutes after coming on as a substitute, his stoppage-time winner automatically takes it place as the greatest moment in his club’s mostly low-key history.To put the achievement in context, Wigan had never progressed beyond the quarter-finals until this season, and they had beaten one of the most financially empowered clubs in the world.Yet the north-west club will not have too much immediate opportunity to celebrate. With two matches to save their Premier League status, they are due back in training tomorrow. The challenge is clear. No team has won the FA Cup final and been relegated in the same season.