Fyvie, celebrating his 17th birthday, had a hand in both goals as the Dons ran out 2-1 winners over St Mirren on Saturday to end their dire sequence of results.
McGhee was delighted with the performance of Fyvie, who came on as a first-half substitute for Derek Young after the latter was taken off suffering from concussion.
McGhee said: "He was brilliant. We didn't play him last week against Dundee United because of the pressure of the game and the boys that came in did so well so he had to start on the bench against St Mirren.
"But he came on early and made a big, big contribution. I think Fraser benefited from getting the rest last week.
"It was his birthday and he was desperate to play and he really showed that when he went on."
McGhee admitted there was an element of luck about his side's second goal, with Sone Aluko's shot taking a wicked deflection before trickling into the net.
However, the Dons boss was quick to point out that you create your own luck in football.
He said: "We haven't lost games because we have been unlucky. It is great to get that bit of luck and it has helped us over the finishing line.
"But we can't claim that we have had bad luck.
"You make your own luck. Perhaps working as hard as we did made that bit of luck for us which manifested itself in a goal."
McGhee believes striker Steve MacLean, who was later sent off for a second bookable offence, got the final touch for Aberdeen's winner, but Aluko naturally disagreed.
"The goal was mine, 100%," the winger said. "Steven was celebrating like he was the one that had scored but I think he was just happy we had scored.
"There is no way anyone is taking it away from me."