Scott Waites joined defending champion Scott Mitchell in the last eight of the BDO World Championships with a stunning comeback win over Geert de Vos.
England's Waites, the 2013 champion, trailed 3-0 in his second-round tie at Lakeside but came back to win 4-3.
Earlier, Mitchell beat pairs partner Mark McGeeney, who missed eight match darts, in a sudden-death leg.
Richard Veenstra of the Netherlands beat Martin Atkins 4-0, while reigning women's champion Lisa Ashton went out.
Nine-time world champion Trina Gulliver overcame Ashton 2-1 in their quarter-final to end the number one seed's hopes of a third successive title.
Dutch fourth seed Aileen de Graaf, England's Deta Hedman and Denmark's Ann-Louise Peters also qualified for Friday's semi-finals.
Peters made a 160 checkout against Zoe Jones, the highest finish in the history of the women's competition at Lakeside.
Meanwhile, England's Josh Richardson, 17, beat Jordan Boyce of the Republic of Ireland 3-2 to win the World Youth Championship.
'Sometimes it's better to be lucky than good'
Sixth seed Mitchell and number 11 seed McGeeney were England team-mates and pairs partners at last year's World Cup in Turkey.
Lakeside debutant McGeeney, 43, took a two-leg lead early in the seventh set but opportunities to win the match were squandered.
Mitchell, 45, did likewise, three times failing to close out the match on his own throw.
At 5-5, McGeeney won the honour of throwing first in the final leg but he could not complete a 102 checkout on double 16, allowing Mitchell to land a decisive double top.
Mitchell said afterwards: "Sometimes it's better to be lucky than good."
Key stats from day six
- Mitchell was victorious in a sudden-death leg at Lakeside for the second successive year. In 2015, he won a first-round tie against Tony O'Shea in the same manner.
- De Vos won all three legs in the second set of his match with Waites with successful shots at the bullseye. However, the eighth seed made a fifth consecutive second-round exit from the BDO World Championships.
- Ashton missed her first 19 attempts at a double in her defeat by Gulliver.
Scott Mitchell: "I really don't want to give this thing up. Averages don't interest me, being in the next round is what interests me. I've got away with this one, but I'm still in."
BBC pundit Bobby George on Mitchell's win: "I thought it would be close, but I didn't think it would be that close. It was a great match to watch, it was so exciting."
Trina Gulliver: "I was very lucky because Lisa missed so many doubles. I was very fortunate to get through, but I enjoyed the game. I'm not finished yet."
All four men's quarter-finals will be played on Friday.
Waites' match with number one seed Glen Durrant is the final game of the day's early session (live on BBC Two, coverage starts at 13:00 GMT), while Mitchell plays Veenstra during the late session.
The two semi-finals in the women's draw - Gulliver v De Graaf and Hedman v Peters - are also due to take place, with the winners progressing to Saturday's final.