World number one O’Sullivan defeated Joe Swail 5-1, while Dott knocked out former Grand Prix champion Dominic Dale 5-2 in Preston last night.
Masters champion Paul Hunter got out of jail against Essex rival Ali Carter. Yorkshireman Hunter, the world number five, trailed 4-2 and was 39-0 down in the seventh.
However, he pulled back from the brink with runs of 53 and 27, shaded a scrappy penultimate frame and then compiled 102 to take the decider.
Hunter’s reward is a match against six-time world champion Steve Davis. Davis became the first player to reach the last 16 by defeating Tony Drago 5-1.
He was joined in round three by Australian Neil Robertson who knocked out Andy Hicks 5-3 in a battle of left-handers.