The McCullough sisters had contrasting fortunes as the Ulster Winter Matchplay tournament got under way at three separate venues in Belfast last night.
The top performers will qualify for the national Matchplay tournament in Dublin next month.
Annie McCullough defeated her Windsor club mate Laura Reid 6-2, 7-5 to advance to the semi-finals of the Under-18 girls event at the David Lloyd Centre in Dundonald.
However there was disappointment for her twin sister Caitlin who went down 7-6, 6-3 to Downshire player Emily Beatty.
Beatty's win represented a triumphant return to the David Lloyd Centre where she won the U18 title at the annual tournament a few weeks ago.
Ulster champion Lucy Octave, from Donaghadee, overcame Windsor 15-year-old Lydia Kelly 6-3, 6-2 to earn a meeting with Annie McCullough in the last four.
Karola Bejenaru takes on Enniskillen's Laura Griffin in the remaining quarter-final today and is hot favourite to earn a date with Beatty in the last four.
Meanwhile, Matthew O'Boyle is safely through to the semi-finals of the boys' event at the Boat Club.
The Bangor player defeated Joe Heatley 6-2, 6-4 and, if the quarter finals go with rankings, he will face Ardghal MacMahon in the last four.
Peter Corrie and Tom Harty also won, beating John Ewing (6-2, 6-2) and Will Millar (7-6, 6-3) respectively.
At Windsor, Ulster U16 champion Ben McClurg won his first two matches in that age group, defeating Matthew White and Anton Robb in straight sets.