Media playback is not supported on this device
They eventually won 3-1 to move eighth - four points above 11th place.
But asked whether Callum Booth's goal 15 minutes from time had started the nerves jangling, McGhee joked they had started long before that.
"At 3-0 I'm nervous; the way we've been we're capable of anything," the Fir Park manager told BBC Scotland.
"That includes losing three goals in the last 15 minutes so I was never comfortable."
Media playback is not supported on this device
McGhee had spoken before the match of the fine margins involved in winning and losing, with many of the teams in the Premiership well-matched in his view.
"It's my turn today to stand here with the points and say my team did well and things went for us," he said after the game. "That is the nature of the league. Next week it'll probably be Partick Thistle.
"We went and beat Dundee United - I felt comfortably - and they've then won their next two games.
"The thing about this division is that we're all capable of winning and losing to each other.
"We needed the three points and we went after it, we played three up front and two very attacking midfielders so we went out to win the game."
Motherwell's victory lifts them above Thistle, who slip to ninth in the table, though they have three games in hand on most of their rivals.
Nonetheless, Thistle manager Alan Archibald accepts they are still very much in the thick of the battle to avoid a relegation play-off.
"We've always been in a battle to survive," he said. "I said yesterday we were three (points) from the top (six) and three from 11th place, so we're very much in it.
"You need to put a good run together to get away from it. We've done that to get ourselves mid-table. With the games called off, we've sunk back down.
"You see how quickly things change. We were eighth before the game and Motherwell have jumped ahead of us again and I think that's going to happen from now until the end of the season."
Mark McGhee admitted Motherwell's habit of shooting themselves in the foot meant that even at 3-0 up against Partick Thistle he could not relax.