The Silkmen continued their fine run in the competition by overcoming higher-league opposition for the fourth successive round - having previously knocked out National League North duo Alfreton Town and Curzon Ashton, before thrashing National League strugglers Dorking Wanderers in the previous round.
Roared on by a sizeable away following, Alex Bruce's side broke the deadlock 13 minutes after half-time when captain Fensome headed home the opener.
Heathcote got in on the act minutes later, confidently firing home his first goal for the club.
Goalkeeper Adam Desbois made a number of fine saves to keep the scoreline down as the National League South side - currently fighting for a play-off spot - were unable to find a route back into the contest.
Speaking post-match, Macclesfield boss Alex Bruce said: "I thought that from the first minute until the very last, we totally dominated the game.
"I'm delighted for them [the squad] and the supporters. It was one of those really good days.
"The weather was horrific on Thursday so we couldn't do much in terms of shape, but we had an idea of how we wanted to play.
"We spoke about it before the game and they executed it perfectly. The players who came into the team gave us something different.
"To a man, I was proud of all of them. "
Macclesfield are the lowest-ranked side to have already confirmed their place in the quarter-finals of the competition, with two fifth round ties still to be played on Tuesday night.
The draw for the last eight will be made on Monday afternoon, and Bruce believes playing against higher-level opposition brings the best out of his side.
"They've shown, especially in the cup against teams from higher leagues, what they're capable of," he said.
"It's about doing that on a consistent basis, and if we can do that, it could be a really good season for everyone involved with the club.
"Two games from Wembley, I've said that to the lads. With the group that we've got, there's no reason why we can't go and achieve what we want to achieve."
Photo credit: Chelsie Wilson