Fletcher's future looked in doubt when he announced in November 2011 that he was taking an extended break from the game after being diagnosed with ulcerative colitis. He managed just 13 appearances in the 2012-13 season to heighten those fears.
"This is it, I'm back for good. This is hopefully the game which means I'm back now," he told the MUTV channel after the win.
"I seem to have come through the setbacks and health issues and I'm thankful for that. It's onwards and upwards now.
"I always believed I would come back, I kept that mind-set. I think other people around me were trying to make me think otherwise, but I stayed strong and believed I would get back."
The Scotland captain replaced Ryan Giggs on Sunday at Villa Park and was given a warm reception by visiting supporters who have seen United struggle in the centre of their midfield this season.
The tenacious, box-to-box midfielder had risen through the club's youth academies before establishing himself as a key member of Alex Ferguson's squad at Old Trafford, winning Premier League titles and the Champions League in 2008 before illness struck.
This, he believes, is the start of a second career with the 20-times English champions.
"Ever since I was a kid, I've wanted to play football. I've been fortunate enough to have the opportunity to play for Manchester United and wasn't going to give that up lightly," Fletcher said.
"I battled through it, and I'm only 29 years old, I think I've got plenty more years of playing left in me.
"I could have a career all over again if I get my health right, and hopefully that's what I'm going to do.
"I'm still building up my fitness, but I don't want to take it easy. I've done enough of that, and I want to be involved, to get us back to where I know we should be."
It has been all change at Old Trafford during Fletcher's time on the sidelines, with David Moyes suffering an indifferent start after replacing club legend Ferguson in the close season.
Many critics feel central midfield has been United's undoing in home losses to Everton, Newcastle and West Bromwich Albion.
Moyes' failure to sign a world class midfielder and the absence of England international Michael Carrick through injury has left 40-year-old Giggs paired with either Tom Cleverly or the versatile Phil Jones in the centre.
Fletcher, though, is ready to help drag United up from their current position of eighth place, 10 points back of leaders Arsenal.
"I think that's the biggest determination for me. It's difficult watching when the lads are winning, but a lot more difficult when they're not winning," Fletcher said.
"I want to help as much as I can, I want to keep picking up minutes, even if it's with the reserves. Ultimately, the goal is to play in the first team, to be a part of the plans, and to bring success back to Manchester United."
Moyes lauded Fletcher's fight in returning to first team action but was cautious about putting too much pressure on his charge.
"Isn't it great that a player who has had an illness like Darren has had can come back and get on the pitch. I know this has happened before and we're not going to get carried away with it, but I think it's a great sign," the Scot said.
"He's looking good, he's feeling good and anyone who saw him today (Sunday) would say that he looks much better and much more like his old self.
"He passed the ball well, kept it for us and was in the right position where we needed him. You can see the talent the boy has."