Following their relegation from the Premier League, the Latics were one of the pre-season favourites for promotion but found themselves 15th in the table when Rosler took over from the sacked Owen Coyle in December.
A 1-0 victory over Birmingham City on Tuesday guaranteed the Lancashire outfit a top-six finish, and Rosler feels that this is a staggering turnaround considering that his side have had to cope with several notable injuries and a run to the FA Cup semi-finals.
He told reporters: "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 and 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."
Wigan appear likely to face fourth-placed Queens Park Rangers in the Championship playoff semi-finals.