Del Rosario blanked Johnsson in their best-of-three match, 278-203, 232-189, to gain a crack at the finals versus second seed Shannon Pluhowsky of the United States.
Pluhowsky made it to the semis with a 223-204, 231-163 whipping of Laura Rhoney.
Del Rosario, the 2003 Asian ranking champion, got off to a blazing start, opening up with nine straight strikes.
There wasn’t much Johnsson could do in the first game but practice and wait for Game Two.
But Del Rosario sustained her good game in the ensuing match, connecting for the first three strikes and, after a spare, made a double.
Johnsson opened in frames 3 and 5 to trail by 55 pins, but Del Rosario stayed clean throughout the next three frames to put the match away in the ninth frame.