McKenzie's former teammate Gerry Melnyk dubbed the young player "Pieface" for his resemblance to a cartoon figure of the same name featured on the wrapper of a popular Canadian candy bar; this was later shortened to "Pie."

In the playoffs that year he scored seventeen points in fourteen games, fourth on the team after Bobby Orr, Phil Esposito and John Bucyk and did so again in 1971-72.

In the summer of 1972, McKenzie was disgruntled at being left unprotected in the expansion draft, and he signed as player-coach with the Philadelphia Blazers of the newly formed World Hockey Association (WHA).

In thirteen games he recorded only two wins and eleven losses, and he stepped down as coach in favor of veteran Phil Watson.

He continued to play effectively for the Blazers, then for the Minnesota Fighting Saints, the Cincinnati Stingers and finally the New England Whalers.