With New Zealand international Stephen Donald sidelined for a month with a knee injury Heathcote, on his 20th birthday, proved a more than capable replacement.
Heathcote had a hand in three of his side's four tries and kicked over seven points to secure a much-needed win for relegation-threatened Bath.
"He's one of several good, talented lads who are helping to make the difference in the first team at the moment," McGeechan said of Heathcote.
"Losing Stephen Donald like that, this is one of these bonuses, that Tom is getting games under his belt.
"He's got that confidence and he knows he has to shape the game. Tom was one of the big plusses today."
While delighted with a five-point haul that eases Bath away from the relegation zone, McGeechan was not getting carried away: "There's two percent difference between top and bottom in this league.
"There are no gimmes. If you are not doing things well, you won't win. Your own game has to be right to get the points.
"We started well and then got a bit careless. And we gave some silly points away.
"The second half was pretty important to the way we came out and came back at them.
"Apart from the try at the end, which was a bit annoying, it was 22 points in the second half. We stuck at it pretty well."
Newcastle director of rugby Gary Gold said: "I am happy with the bonus point but not remotely happy with the outcome. We need to start winning away from home.
"We promised the guys would give their all for 80 minutes - and they did that. We showed a lot of courage and worked hard in defence. We scrambled well.
"But they were much better than us in the second half, so credit to them. Their 'chip through' try was a game changer. Next thing we knew, we were two scores behind.
"We had opportunities too in the second half but didn't take them."
Gold was concerned with the number of penalties his side conceded, adding: "We can improve on our discipline. Silly penalties will hurt you in the Premiership.
"We have to be incredibly tough on ourselves to realise that these penalties can hurt you."
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