Jeff Smith beat ninth seed Gary Robson to qualify for the men's quarter-finals of the BDO World Championships.
The 39-year-old led 3-1 and was pegged back to 3-3 by Northumberland's Robson before winning in a deciding set.
Qualifier Smith is the first Canadian to reach the last eight at Lakeside since John Part won the title in 1994.
Three-time champion Anastasia Dobromyslova and Fallon Sherrock both progressed to the semi-finals of the women's event.
Russia's Dobromyslova, who is based in Ellesmere Port, Cheshire, lost just one leg in her 2-0 win over 22-year-old Zoe Jones from Redditch, Worcestershire.
Sherrock, 20, lost the first set to Dutch third seed Aileen de Graaf but the sixth seed from Milton Keynes fought back to claim victory in a sudden-death leg.
Smith, who is the only overseas player left in the men's competition, missed six darts for the match before finally landing double eight to beat Robson.
"I came out like a house on fire but you've got to give Gary credit where it's due. He came back so hard and it basically turned my legs to jelly," said Smith.
"I had a couple of opportunities to put the match away, but he played so well and I couldn't shake him off."
The men's quarter-final line-up will be completed on Thursday evening, with 2013 champion Scott Waites taking on Ross Montgomery and Jamie Hughes up against Glen Durrant in the two remaining second-round matches.
The inaugural World Youth Championship was won by 16-year-old Colin Roelofs of the Netherlands, who put in an impressive performance to beat Derbyshire's Harry Ward 3-0 without dropping a leg.