Mikhail Grabovski gained the puck in the neutral zone and went in on a 2-on-1 with MacArthur. He glided to the left dot before feeding MacArthur, whose one- timer first appeared to be stopped by Islanders netminder Al Montoya.
However, a review showed Montoya made the glove save but the puck was already across the line, sealing the win for Toronto.
MacArthur also had an assist, while Grabovski had a goal and three helpers and Jake Gardiner finished with a goal and an assist for the Leafs, who have won three of their last four. Jonas Gustavsson made 29 saves in the victory.