The Tigresses and the Lady Spikers square off at 2 p.m., with the winner gaining the momentum when they clash anew in the Final Four on Saturday.
Defending champion National University, which topped the eliminations at 12-2 to secure the first semis bonus, battle No. 4 Far Eastern University also on Saturday.
UST, De La Salle and FEU finished with identical 9-5 slates, as well as in the ranking points tiebreaker with 27 points each.
For having a better ratio than FEU, UST and La Salle will clash for the No. 2 spot.
La Salle beat UST in the semis enroute to winning the Season 85 (2023) title, while UST prevailed last season to reach the finals.
"Even La Salle says the same thing -- they know us well, and we know their staff too. We both know each other's go-to players. It’s going to come down to a battle of mental toughness and heart when we face each other in the playoffs," UST coach Kungfu Reyes said.
UST won, 25-12, 22-25, 13-25, 25-23, 15-13, last Feb. 26, while La Salle prevailed, 15-25, 25-17, 24-26, 25-20, 16-14 last March 29.
Angge Poyos, Reg Jurado, Maribeth Hilongo and Cassie Carballo will spearhead UST, which bowed to NU, 25-23, 17-25, 18-25, 25-22, 9-15, last Sunday.
"You know we're chasing that twice-to-beat advantage, but the learnings we gained here, again, we'll be bringing them with us heading into the semifinals. Like we told the team, we're championship material, but there are still a lot of things we need to fix. Sometimes, it's not even about volleyball skills anymore -- it's more about our foundation, that even just by standing there, you already show strength. That's how NU is -- they really hold on to their veteran presence," Reyes said.
"As for us, we have that too, but we're still lacking in those aspects that need to be developed outside of volleyball. Hopefully, we can still grow in that area because, as we always say, the skills are already there; now we have to develop our maturity and decision-making," he added.
Angel Canino, Shevana Laput, Baby Jyne Soreno, and Lyka May De Leon will banner La Salle, which suffered a 20-25, 26-28, 25-20, 23-25 loss to FEU last April 26.