The home side looked to be coasting when Michael Higdon swept home his third goal in the 69th minute after two early goals.
But Nigel Hasselbaink and Liam Craig beat Lee Hollis within the space of two minutes just after the goalkeeper had replaced the injured Darren Randolph, setting up a nervy finish.
However, Hollis made an excellent late save from Hasselbaink to keep the three points at Fir Park.
McCall said; "It was a really good goal by Hasselbaink and with the players they have in their team, especially in attacking areas, I always think they will be a threat.
"I don't think it was a case of switching off. I felt for Lee Hollis who said he felt a bit like an idiot, he just walked on the park and two goals had flown by him.
"But even if Darren had been in, they were two really good goals. He made a crucial save at the end and a home win against rivals for a top-six spot, we have to be grateful."