Graeme McDowell beat Nicolas Colsaerts in the World Match Play Championship in Bulgaria, gaining revenge for his defeat in last year's final.
Colsaerts had also knocked the Northern Irishman out in 2011, but McDowell made it third time lucky with a 2&1 win in the quarter-finals at Thracian Cliffs.
McDowell now plays Branden Grace who beat England's Chris Wood 2&1.
The other semi-final sees Grace's fellow South African Thomas Aiken take on Thongchai Jaidee of Thailand.
Aiken beat Italy's Francesco Molinari 3&2 while Jaidee defeated Scott Jamieson of Scotland 4&3.
Three up after nine, McDowell seemed set to go further ahead when Colsaerts' drive on the short par-four 10th finished inside a public toilet.
But after taking a penalty drop, Colsaerts pitched onto the green and holed from 15 feet for par to halve the hole.
Colsaerts could be heard laughing as he pleaded with the referee not to make him drop the ball inside a bathroom on live television, but had to drop it twice as it rolled nearer the hole the first time.
"I was laughing because I was going to look like a clown," Colsaerts said.
"I'm going to make 'A Question of Sport' and I'm sure it's going to make the news, some Belgian dude dropping the ball in a toilet.
"It is fun to be recognised for stupid stuff like that."
After escaping with his par, Colsaerts got back into the match with a birdie on the 13th - where McDowell was going to drop at least one shot - and by winning the 14th with a par.
However, he missed a birdie putt from seven feet on the 16th to get back on level terms and then hit two clumsy pitches on the par-three 17th to allow McDowell to close out the win.
Branden Grace (Rsa) beat Chris Wood (Eng) 2&1
Thomas Aiken (Rsa) beat Francesco Molinari (Ita) 3&2
Thongchai Jaidee (Tha) beat Scott Jamieson (Sco) 4&3
Graeme McDowell (NI) beat Nicolas Colsaerts (Bel) 2&1