The Oman international has been one of the Latics' standout players since joining, initially on loan, from Bolton in 2010, and Martinez felt the responsibility for the defeat lay with the whole team.
The Spaniard said of Al Habsi: "He's a really solid character and a player who represents what we want to do.
"He's got an infectious attitude, the way he works, the improvement he's brought to his own game is the ethos and mentality we've got at our football club.
"As a player you're going to have good days and bad days but he's always wanted to improve and to take responsibility.
"Ali's been in tremendous form and I think on Saturday as a team we dropped our standards, probably that little intensity that you need wasn't there, and we let ourselves down.
"I don't think he dropped his level more than the others. The last man is going to be the one who's highlighted but the pressure on the ball all the way to the goal wasn't good enough."