The Scot struck his first goal for United in just over a year to help his side come back from a goal down to pile the misery on rock-bottom Rangers.
"Everyone is delighted," said Ferguson of Fletcher.
"It has been a long road back for him. It is the first time he has played twice in one week. He didn't let us down again. He never does.
"It is lovely to have him back like that. We will look at Wednesday but he has made a great contribution today.
"We played for 10 or 15 minutes. That was the sum total of our real performance from Manchester United.
"Of course it is frustrating we keep ending up in that position but when they scored it definitely sparked us up."
Fletcher played down his contribution, adding: "The only thing it meant was that it put us in front.
"It is great coming back and scoring goals but you want to be on winning teams. When we went behind I thought 'oh no, here we go'. But the lads always respond."