An unforgettable day at the Lakeside started with former two-time champion Waites coming from 4-1 down to beat Andy Baetens, who missed six match darts.
The Belgian's first two chances to reach the semi-finals on his debut came when leading 4-2 and he spurned the other four when leading 2-1 in the deciding ninth set.
Waites then produced a brilliant leg against the throw to move ahead at last, and a trio of 140s helped him down to 36 for the match, which he hit at the second attempt.
It was hard on Baetens, who should have earned a semi-final place and was visibly distressed after failing to do so.
"I always battle to the end," said Waites. "To be honest, Andy was absolutely awesome the first few sets. The more of these games you play, the more experience you get. He was by far the better player. I should be out now."
The beaten man predicted that Waites would go on and win the title.
"I played very well on this stage - I will be back," said the Belgian.
Top seed, defending champion and tournament favourite Glen Durrant provides Waites' next test after overcoming the challenge of our 50/1 tip Jim Williams with a 5-4 victory.
Durrant, like his semi-final opponent Waites, battled back from a 4-1 deficit with the deciding set proving simple for the Teeside thrower as Williams saw his hopes of victory slip away.
When 4-1 down, Durrant went on to win 12 of the next 13 legs thanks to a fantastic spell of darts. He won the sixth set in just 38 darts, the seventh without reply and levelled the match at 4-4 with a 116 checkout.
Welshman Williams had 180s in each of the opening two legs of the deciding set, but Durrant found a response and won the set 3-0 for the match.
He finished with the first 100+ average at the Lakeside since 2014 and the 21st in the tournament's history dating back in 1978.
"I’m so emotional," Durrant told Channel 4 after his win. "Jim is fantastic, he should have won this match, so it’s bittersweet in that sense. But I can’t believe how happy I am. I’m the best friend of Jim Williams and he’ll be hurting now but he’ll be world champion one day."
While one of our in-form darts tipster Chris Hammer's selections fell in agonising circumstances - another rallied to claim a comeback victory during the evening session.
That was BDO number one Mark McGeeney, who was backed at 25/1 each-way, as he battled back from 3-1 and 4-3 down to defeat Wayne Warren of Wales.
McGeeney took the opening set but was blown away by a succession of 180s from the heavy scoring Warren over the next three sets.
After pulling one back, two impressive checkouts of 122 and 154 helped him square the match only for his opponent to edge ahead once more.
McGeeney held his nerve to take the fifth leg in the eighth set to force a decider, which he won by two clear legs 4-2 to advance.
He will next face the unseeded Michael Unterbuchner, who once again upset the odds to defeat Richard Veenstra in another epic encounter.
Unterbuchner won four sets on the trot after dropping the first two only for Veenstra to storm back and force a deciding set, which the German won 3-0.
In the women's competition, defending champion Lisa Ashton will face Anastasia Dobromyslova in the final after they saw off Deta Hedman and Trina Gulliver respectively by 2-0 scorelines.
Friday results & Saturday schedule
Friday Afternoon Session (1pm)
Quarter-Finals (Best of 9 sets)
- Scott Waites 5-4 Andy Baetens (13)
- Trina Gulliver (7) 0-2 Anastasia Dobromyslova (6) (best of 3 sets)
- Glen Durrant (1) 5-4 Jim Williams (9)
Evening Session (7pm)
Quarter-Finals (Best of 9 sets)
- Deta Hedman (1) 0-2 Lisa Ashton (4) (best of 3 sets)
- Richard Veenstra (11) 4-5 Michael Unterbuchner
- Mark McGeeney (2) 5-4 Wayne Warren
Saturday January 13
Afternoon Session (1pm)
Semi-Finals (Best of 11 sets)
TV Coverage: Channel 4
- (4) Lisa Ashton v Anastasia Dobromyslova (6) (Women's final, best of five sets)
- (1) Glen Durrant v Scott Waites
Evening Session (7pm)
Semi-Finals (Best of 11 sets)
TV Coverage: BT Sport
- (2) Mark McGeeney v Michael Unterbuchner
Related links
Fast Results
Scores
Racecards 
