The Lady Falcons got their bearing in the fourth inning, as Rusia belted a two-run homerun - her second this season - to give the reigning seven-time champions a 2-0 lead.
Adamson University will shoot its six-game sweep of the first round against University of the East at 11 a.m. on Thursday at the same Malate venue.
National University rallied past University of Santo Tomas, 3-2, in the other game. The Lady Bulldogs joined the Tigresses, who also lost to the Lady Falcons in a rematch of last year's Finals Saturday, and the Lady Warriors in second place at 3-2.
The Lady Maroons absorbed to their third successive loss after a 2-0 start.
De La Salle University needed a strong showing in the fourth inning to beat Ateneo, 8-1, for its second win in five contests and tie UP in fifth spot.
Baseball action Sunday saw De La Salle outslugging NU, 17-5, to grab the solo lead at 3-0.
In other games, Adamson University stunned defending champion Ateneo, 7-3, while UST downed UP, 9-5.
The Falcons and the Growling Tigers forced a three-way tie in second place along with the Blue Eagles at 2-1.