Vale's prolific marksman Tom Pope lifted a scrappy start to the contest when he tucked away his 16th goal of the season in the 27th minute.
Dale striker Bobby Grant crashed a 30-yard shot against the crossbar in first half stoppage time, but Vale were full value for their interval lead.
In the 62nd minute Pope collected Williamson's low cross but still had plenty to do as he swivelled into space and lifted a 12-yard shot into the top left-hand corner of Lillis' net. Sam Morsy was then shown a straight red card for a dangerous tackle on Jason Kennedy in the 66th minute and the youngster's indiscretion threw the visitors a lifeline.
Grant reduced the arrears in the 73rd minute when he headed in at the far post after Phil Edwards swung over a long cross from the right.
And Andrew Tuttle equalised four minutes from time with a terrific 20-yard shot into the top right-hand corner of Chris Neal's net after a short corner from Ashley Grimes.