Patrick Rooney, a teenage squash professional from St Helens in Merseyside, left Welsh squash fans disappointed at Rhiwbina SRC.
The 19-year-old Rooney, ranked 104 in the World, defeated home favourite Peter Creed in four games.
Caerphilly-born Creed, who plays out of the Rhiwbina club, won the first game 11-6, but Rooney hit back to win the next three 11-8, 11-5, 11-6.
Eighth seed Rooney joined the PSA World Tour three years ago, won silver at the Commonwealth Youth Games in Samoa during 2015 and gold in the European Junior u-19 Championship.
He plays Leicester-born George Parker in the Rhiwbina PSA $10,000 World Tour Tournament final in Cardiff.
Qualifier Parker, 21, defeated top seed and fellow Englishmen Joshua Masters in his Welsh Open semi-final, winning 11-8, 11-9, 11-9.
The Rhiwbina event attracted players rated in the World’s top 100.
Attendances have been excellent all week and the semi-finals were sold out.
First round results, seedings in brackets:
(1) Joshua Masters (England) beat Lyell Fuller (England) 10-12, 11-4. 11-6, 11-8
Ahsan Ayaz (Pakistan) beat (5) Kristian Frost (Denmark) 7-11, 4-11, 11-5, 11-6, 11-9
(Qualifier) George Parker (England) beat (6) Jan Van Den Herrenwegen (Belgium) 11-4, 7-11, 11-9, 11-8
(4) Mahesh Mangaonkar (India) beat (Qu) Emyr Evans (Wales) 11-8, 10-12, 11-1, 10-12, 11-6.
(3) Carlos Cornes (Spain) beat (wildcard) Sam Fenwick (Wales) 11-6, 11-9, 11-6
(Qu) Mark Fuller (England) beat (8) Patrick Rooney (England) 14-12, 11-4, 11-6
Ammar Altamimi (Kuwait) beat (7) Dougie Kempsell (Scotland) 12-10, 8-11, 11-8, 12-10
(2) Peter Creed (Wales) beat (Qu) Brian Byrne (Ireland) 11-3, 11-3, 11-3
Quarter-final results:
(1) Joshua Masters beat Ahsan Ayaz 11-7, 11-7, 11-7 (33 mins)
(Qu) George Parker beat Mahesh Mangaonkar 6-11, 11-3, 11-3, 11-6 (44 mins)
(8) Patrick Rooney beat (3) Carlos Cornes 9-11, 11-7, 11-2, 9-11, 11-4
(2) Peter Creed beat Ammar Altamimi 11-6, 9-11, 11-7, 11-5 (53 mins)
Rhiwbina PSA Semi-finals:
George Parker beat Joshua Masters 11-8, 11-9, 11-9
Patrick Rooney beat Peter Creed 6-11, 11-8, 11-5, 11-6
The final is at Rhiwbina SRC on Sunday (3pm).