The holders have now qualified for the quarter-finals of the competition and set up a rematch of last year's final against Manchester City after Saturday's 2-1 victory over Cardiff City.
Watson, who scored the winner at Wembley in May and was on target with the crucial goal in south Wales no Saturday, applauded the impact that Rosler has had on their form.
The Latics are sitting in ninth position in the Championship and could find themselves just a single point off the final play-off position if they win both of their games in hand.
Speaking to the Daily Mirror, the 28-year-old said: "The gaffer has been great since he came in and his record has been great.
"He has us organised and we are playing the way we want to play. If we beat Barnsley, we're a point off the play offs - and in the quarter finals of the FA cup, so the season is starting to look up.
"Having success in the FA Cup is special. Once you've won it. It's an amazing feeling. It's anyone's to win, as we proved last season. We're in the quarter-finals against City, which no one expected us to do."
Watson also spoke out of his delight of constantly grabbing the cup headlines, adding: "I never get bored of being a cup hero - I love it, it's great.
"People can call me a cup hero and all that but the thing about this win was it was about the whole team. We were brilliant."