The 30-year-old, who signed for the Latics last year following a season-long loan from neighbours Bolton, has made two errors in his last two matches, but Martinez played down any concern over his form.
Al Habsi's blushes were spared against Reading last weekend when Jordi Gomez's last-minute winner took the focus away from the keeper's blunder after the ball bounced off him and into the net to make it 2-2.
The Oman international then failed to deny Manchester City striker Mario Balotelli on Wednesday night after he blocked Gareth Barry's shot from the edge of the area and stopped Balotelli's initial follow-up, but could do nothing with his second strike.
However, Martinez was quick to deflect any criticism away from his keeper.
"I don't think it was an error (against Manchester City)," the Wigan boss said.
"Ali in my eyes is one of the best in this league.
"Sometimes you expect Ali to save the unstoppable and that's very unfair.
"The shot from Gareth Barry was moving away a little bit and he came up with a world class save in the rebound but the unfortunate point is that the ball bounced straight into the striker's path and not the defender's path.
"I don't think that's a mistake at all. That's a little bit of misfortune.
"This new ball is quite tough for goalkeepers. His reaction for the first save was outstanding."
Martinez is confident his first-choice keeper will put any demons behind him for Monday's trip to Newcastle.
"Ali is such a confident player and internally he is a very strong human being," Martinez said.
"I would say his mental strength is his biggest quality.
"As a goalkeeper you need to be able to move on from action to action and he is not affected by that. It's not a confidence issue at all."
Martinez still has a host of injury problems to contend with for the clash at St James' Park despite an extra 48 hours of rest.
The Spaniard rated both defender Gary Caldwell and midfielder David Jones as "50/50" for the match, leaving him with eight players potentially ruled out through injury.
Jones picked up a knock to his calf during Wednesday's 2-0 defeat by Manchester City while Caldwell is recovering from a hamstring problem.
Midfielders Albert Crusat (knee) and Ben Watson (broken leg), winger Ryo Miyaichi (ankle), forward Shaun Maloney (groin) and defenders Antolin Alcaraz (groin) and Ivan Ramis (hamstring) remain on the sidelines.