Rosler's side, who have a Wembley date with Arsenal to come next month, had dropped two league points in midweek after conceding a stoppage-time equaliser against Yeovil.
But the FA Cup holders got back to winning ways with a home win their manager reasoned was entirely merited.
Lewis McGugan gave the Hornets the lead against the run of play after 36 minutes.
"We had the majority of the possession and far more attempts on goal," said Rosler.
"Even before they scored, we had three massive chances - two of them one-against-one.
"I felt we were very unfortunate to go a goal down, but we had to sort out one of two things defensively.
"We did that in the second half and, apart from the last 10 minutes when they changed their shape and went more direct, I don't think they caused us many problems.
"We didn't panic when we went 1-0 down, we carried on playing, and I felt we had chances in the second half to kill the game off completely.
"With the match programme, we are looking a little heavy, and we could have done with the two-goal cushion.
"But overall I am very happy."
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