Rosler said: "We knew that with four games to go in the season we knew we needed one win.
"It was a monumental effort from the squad - starting on the 9th of December being 15th in the league.
"We had a mountain to climb to catch up in addition to that we had a fantastic FA Cup run.
"A lot of people said that it was impossible for us to achieve the play-offs with that cup run and we did by utilising the squad and managing players coming back from long-term injuries - Ivan Ramis, Gary Caldwell, Shaun Maloney, Roger Espinoza.
"Without utilising the squad, without everyone contributing to make that effort successful to overcome the first hurdle, it is a big compliment to the players.
"It was only possible, the way that we did it, by everybody contributing and I am very proud of my players.
"We will now have two days of active recovery. We are not shutting down the engine completely.
"We will make sure that we will have a very strong and motivated team pushing for a win at Blackburn Rovers."
Wigan stunned Birmingham when City paid the penalty for allowing Jordi Gomez to run unchallenged with the ball to the edge of the area before picking out McManaman, whose low shot curled beyond the outstretched left-hand of goalkeeper Darren Randolph.
Ironically it was the only time that Wigan really threatened with Randolph's opposite number, Scott Carson, ensuring that Rosler's side held on to the win.
The former England international denied Emyr Huws with a stunning one handed 29th minute save before frustrating Federico Macheda and Hayden Mullins as Birmingham launched a late search for an equaliser.
Despite his side's perilous position, Birmingham's manager Lee Clark remains in defiant mood - vowing to keep on fighting for the club's fans.
Clark, whose side have failed to win any of their last 18 home games stretching back to October, knows that even a win against Bolton in Saturday's final game of the season may not be enough to save them after they were caught cold against Wigan.
He said: "We deserved something but we never got the breaks.
"It is never ideal, your game plan, when 90 seconds into the game you are 1-0 down.
"But the players kept fighting and kept working hard. It wasn't to be.
"We have to go to Bolton now and get a result and hopefully at least one other result goes in our favour.
"I have been amazed in the two years that I have been at this club with the support from the terraces.
"The fans are magnificent, but they even surpassed that tonight.
"They took it to another level. The support for the players was astonishing.
"That is who I am gutted for in all this. They deserve better. They don't deserve to be in this position.
"The players are believing but like I have said many times, don't talk the talk, walk the walk. Get out on the grass and deliver what has got to be delivered and that is what I will be looking for."