The result means that QPR are favourites to progress to the final as away goals do not count in Football League playoffs.
Rosler told reporters: "The pressure's on QPR now. We knew it would be a tight game. We're not scoring too many goals at the moment. The positive thing is we got a clean sheet, we controlled the game.
"At times I felt we could have been a little braver in terms of filling the box with more people, having the wing-backs a little bit higher up.
"We had two or three big chances and in games like that, when you play against top teams, there will be not many chances and you have to take them. They came here to get a draw and they got that. I still count our chances as 50-50."
The second leg will take place at Loftus Road on Monday.