Stevens secured a 7-1 advantage and barring disaster when the match resumes this afternoon will reach the last four of a ranking event for the second tournament running.
On the receiving end of the 20-year-old Welshman's brilliant showing was Martin Dziewialtowski. The Scot was already 6-0 behind before winning his first frame and Stevens rubbed it in by clearing up with 66 to win the eighth frame on the black.
Stevens, the world No 53, said: "I've put in a lot of hard work this season, now it's paying off. Whenever I'm in among the balls I feel like scoring heavily."