After clawing their way out of the bottom three last week, Wigan are back in trouble following a 3-2 home defeat by Sunderland.
Martinez blamed the setback on the knee injury Ivan Ramis suffered at Fulham last week, which led to a defensive frailty, with Steven Fletcher moving onto 10 goals for the season with an impressive first-half double.
But Martinez is adamant that, after eight years in the top flight, no-one at Wigan is resting on their laurels.
"We never take anything for granted," he said. "If we had done that we would never have had eight seasons at this level.
"Today we weren't good enough defensively for 30 minutes. We need to rectify that. Ivan Ramis' injury last week cost us today's points. That is something I need to correct."
Wigan went ahead through own goal from David Vaughan, before the visitors levelled through a Craig Gardner penalty.
Steven Fletcher then sent Sunderland on their way to maximum points, his superb one-two making it six goals in seven appearances against the Latics for the Scot.
His first owed much to his lightning reactions after Ali Al Habsi had turned away his header, with the second an instinctive curling strike from Adam Johnson's lay-off.
New-boy Angelo Henriquez scored a late consolation for Wigan, nodding home Shaun Maloney's far-post cross 11 minutes from time.
- Sports & Recreation