Roberto Martinez was again left to rue a controversial decision from the officials that cost his Wigan side at the Liberty Stadium.
After falling 2-0 behind in the second half to goals from Spaniards Pablo Hernandez and Miguel Michu, Wigan grabbed one back after Emmerson Boyce acrobatically turned the ball home.
Two minutes later the ball was crossed from Jean Beausejour, and striker Arouna Kone headed home.
However, an assistant referee flagged for offside as the ball hit the net, despite replays showing that the striker was level.
After a recent fine for criticising officials, Martinez was more philosophical in his thoughts than previously.
"It's a big call," Martinez said. "When I was watching live, it looked level.
"It's an extremely tight decision, and it's a shame because it was an outstanding piece of play. Sometimes these decisions just don't go in your favour."
Wigan now sit in 15th position in the Premier League, with five points from their eight games.