The Dens Park boss is adamant the "job is nowhere near done" as they bid to move a step closer to a return to the top-flight.
Goals either side of the break from Jordan McGhee – both from magnificent Charlie Adam assists – put the Dark Blues firmly in the driving seat.
And a third from substitute Osman Sow six minutes from time ensured Raith have a mountain to climb in the second leg on Saturday night.
McPake said: "Other than a 10-minute spell the game-plan worked. We nullified most of their threats and we were excellent, to a man – even the three subs. They knew their roles and the trust they have in each other, they were outstanding.
"Charlie Adam – how he sees it, I couldn't have done anything like that.
"You've got to look at the runs as well. We scored the same goal on January 2 against Hearts when Jordan headed in. It's something we work on.
"You have someone with the range of passing of Adam, and teams are worried of Paul McMullan's runs. Adam can see a pass where he's the only one who sees it.
"But the whole team were excellent and Charlie would be the first to say that.
"It's half a job but we're nowhere near done. We're in control but there's a long way to go. They're a good side."
Raith were well beaten by the end but were left cursing a potentially pivotal moment just before half-time when Reghan Tumilty had a goal disallowed.
Television replays showed the full-back was well onside when he ran on to Lewis Vaughan's centre for what, at the time, would have been an equaliser.
Manager John McGlynn said: "I didn't think there was much in the first half. It was very close but then there was one piece of magic from Adam and a finish from McGhee.
"Overall the difference was Adam and the balls he played were magnificent.
"The big talking point is the goal we scored and didn't get. It was a perfectly good goal, it wasn't offside.
"I don't think there was much in the first half but to come in at 1-1 would be a better situation than 1-0 down.
"It's a sore one but we have to take it on the chin. Teams have come back from 3-0 down in individual games before.
"It's a big ask but if we don't have a go we're beaten and out. We might as well have a go."