Riis met a cross from Brad Potts flush on the volley and found the net to earn a point.
It was the second time Riis had equalised in the game, the Robins having taken the lead first through Chris Martin and then Antonie Semenyo.
Here are the player ratings from the Championship clash, with Riis pick of the bunch.
13. Ali McCann 7
He brought energy and drive to the midfield after coming on at the interval. What a tackle to set the ball rolling for the late equaliser. Photo: Camerasport
14. Ched Evans 5
The striker replaced Cameron Archer. North End weren’t able to get him into the game as they would have liked. Photo: Camerasport
4 / 4