The South African, who had been out of action since August with a hamstring problem, came off the bench to score with his first touch.
"First touch and back of the net is quite an impact," Martinez told reporters.
"Steven Pienaar brings something really special to our side, for many reasons - firstly the understanding he has with Leighton Baines and also the way he can find space.
"We knew he couldn't play 90 minutes but the impact he had in the game was terrific. It was important for us to have that little bit of magic to get that second goal."
The Toffees are sixth in the Premier League.