The Latics were in front twice but eventually succumbed to a Dwight Tiendalli winner with 15 minutes remaining, leaving them still three points adrift in the relegation zone.
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"I thought we had everything under control from the first half, I thought we were performing very well," he told Sky Sports.
"We had so many injuries at the back that showed today too much. Sloppy goals were unfortunate, but you could see the effort and desire to win the game. Key moments in the game - they affect the result.
"It was such an important game for us and when we make mistakes it becomes a much bigger mountain to climb, what we need to do we get ready for next two games."
Wigan travel to Arsenal next week before hosting Aston Villa on the final day in what could prove to be a vital 90 minutes for the club, and Martinez still believes his side has the character to beat the drop.
"The team is ready to bounce back and take opportunity over the next two games," Martinez added. "We missed an opportunity tonight obviously playing at home.
"We have got incredible character and are determined to fight for every point.
"There are six points to fight for, we have to learn from this - today we need to accept nothing went our way [so] we turn it quickly."