The Latics climbed up into the play-off places following their emphatic 4-1 success over promotion rivals Forest at the City Ground.
Wigan secured a fifth consecutive win to lift themselves into sixth - but manager Rosler has told his players they must not rest on their laurels.
"These teams above us are now in our sights," he said. "We should not be happy just to stay in the top six, we want to catch the guys in front of us. Automatic (promotion) is a little optimistic, but I am talking about the teams who are third, fourth or fifth.
"I said March and April would be decisive. We knew this would be the time of the year when the prizes were earned."
Martyn Waghorn put the visitors in the lead in the first half, before setting up a goal for Emmerson Boyce in the second, after Jamie Paterson had fired the Reds level.
A spectacular third goal from James McArthur was followed up by an even better one as Jordi Gomez smashed a breathtaking 20-yard shot high into the corner of the net in the 90th minute.
And the manner in which his side kept going until the final whistle delighted Rosler.
"It was great to see that. In the second half we were clearly the better team, we scored good goals," he said.
"But the best thing for me was the last 10 minutes, when we pressured them high and forced them into more mistakes.
"Forest have a lot of injuries, but we also have seven players out. All top players who are out for weeks and months. Today, two strong teams played against each other, with enough depth and quality and we won it."
Forest boss Billy Davies insisted that automatic promotion was not beyond his side, despite seeing second-placed Burnley open up an 11-point advantage over them.
"The fact that we are still in the top six with so many players out tells you how well the team has done so far this season," he said. "We are now relying on our under-21 coach, in Jonathan Greening, to play in midfield, tells you exactly what our position is.
"There are 13 games to go and I have said all along there will be twists and turns. Until it is mathematically impossible, then anything is possible. We will continue to be positive.
"I have told the players to keep a spring in their step. To be in the top six when we have so many players out - that is why we have to be very positive."