In a repeat of last year's final - which 22-year-old Ashour won - Matthew came from behind in both of the opening two games to take a 2-0 lead in the PSA Super Series event.
But his victory celebrations at the University of Richmond in Virginia were slightly tempered when Ashour had to retire hurt due to a niggling injury in the third, handing Matthew his third major title of the year.
"It's a strange feeling right now – you feel you should be happy and celebrating, but it's never nice to win like that," said Matthew.
"All credit to Ramy, though - you could see he wasn't moving well. But to come through as far as he did was amazing – I don't think anyone else in the world would have been able to do that.
"It's very tough playing Ramy – you want to keep him at the back because at the front he's lethal. But you also have to attack or you're never going to win a point.
"I got a bit lucky at the end of the second – but that win was crucial. If it had gone one-all, then maybe he would have got his confidence back."
Sheffield-born Matthew fought back from 9-7 down in the first game and 7-4 behind in the second to break the resolve of the struggling defending champion, who finally called it a day to leave a final scoreline of 11-9, 16-14, 5-4 after 48 minutes of typically intense squash.
Afterwards, Ashour - who pipped Matthew to the PS world No 1 slot after defeating him in December's Saudi International final - was quick to veer away from using his injury as an excuse for his defeat.
"He played a terrific match and was a lot better than I was," said ashour.
"It was one of the biggest matches I've ever played in my life. It's good to have each other at the top – pushing each other all the time."
The victory isn't expected to be enough to give Matthew the world No 1 ranking he so craves when the new list is released at the beginning of March, however, although he has drawn level on points with Yorkshire rival James Willstrop - who he defeated in the semi-final - in the PSA Super Series 2010 rankings.