The Ibrox men now boast a 14-point lead at the top of the third flight with a game in hand.
Fraser Aird, Nicky Clark, Nicky Law and Robbie Crawford all scored in their Fife romp as the league leaders responded to the Boxing Day draw with Stranraer which cost them their 100 per cent record.
But McCoist insisted he would not disrespect Monday night's hosts by announcing his side as champions-elect with 19 games still remaining.
He said: "I can't say the league is over and I never would say it and be disrespectful to the opposition.
"But what I will say is that was a big three points for us. Coming off the back of the Stranraer result, everyone was looking to see how we would react.
"We were playing the team closest to us and they were making one or two noises about the game. They felt they were unlucky in the last game at Ibrox and they are a good team.
"But I felt the better team won on the night - there's no doubt about that. It was the complete opposite from Stranraer. I was delighted from start to finish."
Just two years ago, this fixture took place in the top flight.
Both sides ended up as the losers of the fall-out from the Rangers liquidation crisis, with the Light Blues expelled to the Third Division and the Pars defeated in their claim that they should be spared relegation from the SPL as a result.
But the 18 months that have passed since had done nothing to dilute the mutual bitterness between the opposing supporters, and as they hurled insults at each other the aggression was mirrored as Dunfermline bossed a frenetic opening 20-minute period.
"It was like an old-fashioned cup tie atmosphere," said McCoist. "There's been a lot of hostility towards our club and that was the case tonight. We used to love that and our boys looked like they loved it too."
Aird quietened the home support at East End Park after 22 minutes as he drove forward from Law's pass before smashing a 20-yard drive into the bottom corner.
Clark then pinched Jon Daly's goal six minutes after the break when he added a final touch on the goal-line to the Irishman's net-bound header while substitute Lewis Macleod measured a superb through ball for Law to prod beyond Pars goalkeeper Ryan Scully with 20 minutes left.
Daly was the provider again in stoppage time as his knock-down sat up for Crawford - another second-half replacement - to blast home from 15 yards.
Dunfermline boss Jim Jefferies admitted his side were culpable for the goals they lost but praised his young teams' commitment.
"We contributed to some of the Rangers goals with sloppy mistakes but they are young boys and I hope they can learn from it," said the former Hearts manager. "But as far as commitment, as far as having a go, I thought they were tremendous.
"They worked their socks off and had some good spells of passing but you don't get away with the mistakes we made against a side like Rangers.
"The criticism that they got after the Stranraer match was always going to fire them up and they showed us respect by playing well.
"But we had a couple of great opportunities in the first 20 minutes and there are a lot of positives for us to take out of this."