Defending champion Scott Mitchell and top seed Glen Durrant were both knocked out in the quarter-finals of the BDO World Championships.
Sixth seed Mitchell, 45, lost 5-3 to unseeded Dutchman Richard Veenstra.
Veenstra will face Canada's Jeff Smith, who beat Dennis Harbour 5-2, in the last four at Lakeside.
Ex-champion Scott Waites beat Durrant 5-4 and plays Jamie Hughes, who beat Wesley Harms 5-1. Deta Hedman and Trina Gulliver meet in the women's final.
Number three seed Hedman did not lose a leg in her 2-0 semi-final victory over Denmark's Ann-Louise Peters, while nine-time champion Gulliver won 2-1 against Aileen de Graaf of the Netherlands.
Mitchell's reign ends
Mitchell has been one of the most popular world darts champions ever and he has packed plenty into the 12 months since he became the best in the BDO - countless exhibitions, charity functions and an appearance on BBC's Countryfile to name a few.
Neither he nor World Championship debutant Veenstra were at their best, with both unable to consistently replicate the form that got them to the quarter-finals.
Mitchell fell 4-1 behind and although he attempted to mount a comeback, the Dutchman held his nerve to end the title reign of "Scotty Dog" at Lakeside.
Comeback kid Waites downs Durrant
Waites is making a habit of grand fightbacks at Lakeside in 2016. Only 18 hours before his quarter-final with Durrant, the 2013 champion had been 3-0 behind against Geert de Vos and somehow pulled through to win 4-3.
Lifted by the support of the Lakeside crowd, Waites came from 4-2 behind to secure a place in the last four.
A shoulder injury has prevented the 38-year-old from playing anywhere near his full potential in the past couple of years. He says he is pain-free after surgery, although it will be interesting to see if the exertions of two thrilling contests will have any effect during Saturday's semi-final against fourth seed Hughes (live on BBC One, 14:30 GMT).
As for Durrant, it was a second crushing loss in the space of 12 months at Lakeside. He was beaten 6-5 to Martin Adams at the semi-final stage last year but recovered to win six BDO ranking titles in a superb 2015.
If anything, this defeat will have hurt even more, given he is the BDO's world number one and was a strong favourite for the world title.
Key stats from day seven
• Jamie Hughes is the highest seed left in the men's draw at Lakeside. Glen Durrant's quarter-final exit means the top three seeds have all been eliminated.
• Jeff Smith is into the semi-finals at Lakeside for the second year in a row. He reached the last four on debut in 2015, but lost 6-0 to eventual champion Scott Mitchell.
• Trina Gulliver will make her 12th appearance in a World Championship final on Saturday. She played in the first 11 finals at Lakeside (2001-2011), winning nine of them.
Scott Waites: "It's not over until the last dart's thrown. What a game of darts. Glen took his chances early on and that was the difference. Later on, he seemed to give me a shot at double and I took my chances then."
BBC pundit Bobby George on Waites' win: "Scott did it when it counted, but he did the same [against De Vos] on Thursday. I said he could come out and win it from being 3-1 down at the break, but not with the way Glen was playing. It turned out to be a really exciting game."
Jamie Hughes: "That's what I've been waiting for all week. I've been saying that if I clicked, someone was going to get a right hammering. That's given me a massive confidence boost."