A disappointing Chelsea held off a determined Wigan to grind out a win courtesy of Deco's 25-yard free-kick.
The midfielder scored after just three minutes when he found the top corner after Lee Cattermole had handled.
But Wigan hit back and Blues keeper Petr Cech had to pull off smart saves to keep out shots from Wilson Palacios and Amr Zaki.
Chelsea struggled for form but held on for a win as Cech again rescued them by keeping out a late Olivier Kapo strike.
The Blues had steamrollered Portsmouth 4-0 in their season-opener last week and Wigan seemed in danger of a similar fate after conceding an early lead.
Wigan keeper Mike Pollitt, who was a late promotion to the starting line-up following an injury to Chris Kirkland in the pre-match warm-up, may have been disappointed not to have kept Deco's effort out.
But Chelsea were uninspiring overall and the goal proved to be a rare moment of quality from the visitors.
In contrast, Wigan were galvanised by going behind and responded by taking the game to Chelsea.
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Latics left winger Palacios gave Chelsea a taste of things to come when he wriggled his way past Jose Bosingwa and angled in a drive, which Cech blocked away.
Jason Koumas then showed his eye for a pass when he played Zaki through on goal but the Egyptian's well-struck shot was parried by Cech.
The loose ball just evaded the on-rushing Emile Heskey, who would have had the simple task of sidefooting in if Cech's save had rolled into his path.
Cech pushed Emmerson Boyce at a corner and escaped conceding a penalty and, although Ricardo Carvalho headed over at the other end, Chelsea struggled to match the tempo of the JJB Stadium side.
Wigan's quick passing and a clever Palacios backheel gave Zaki another sight of goal and Cech had to save well to keep out his shot.
The Latics' failed to carry their early enthusiasm into the second half as Chelsea nullified their threat..
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