The regular season just sets the seeding for the MPSF tournament. The winner of the tournament gets an automatic invitation to the NCAA tournament. I'm not sure if things might change (things DID change for the men), but last year 3 MPSF teams went to the NCAA tournament. If the only losses for USC, UCLA, and Stanford are amongst themselves, then I'd presume those 3 teams go. If one of them wins the MPSF tournament, they'll presumably be the #1 NCAA seed.
So, while the #1 seed for the MPSF tournament has the easiest road to the NC, they still will have to win two games against the #2 or #3 seed (one at MPSF and one at NCAA).  The #2 & #3 MPSF seeds can win the NC by winning three (or maybe just two) such games (two at MPSF and one at NCAA, or one (or zero) at MPSF and two at NCAA).Â
Stanford still has an MPSF game next weekend against San Jose State. IF Stanford wins, and USC beats UCLA, then three MPSF teams will finish the season with one loss, and the tie breakers kick in.
I believe the tie breakers are described at
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http://www.collegiatewaterpolo.org/club/...akersystem
So, if UCLA beats USC, then
  the MPSF seeding is 1. UCLA (undefeated),
2. Stanford (based on beating USC), 3. USC.
I believe UCLA must beat USC to be seeded #1.
If USC beats UCLA, then it depends on the score.
 In conference play, Stanford beat USC 12-8; UCLA beat Stanford 10-9.Â
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If I understand how score differential is computed, Stanford's differential score is 21-18, +3. Stanford has 21 goals.
 Currently, USC has a differential of -4, with one game to make it up to +3 or better.
 If USC wins by 6 goals or less, then
   the MPSF seeding is
1. Stanford (goal differential), 2. USC (head to head), 3. UCLA
 If USC wins by 8 goals, then
   the MPSF seeding is 1. USC (goal differential), 2. UCLA (head to head),
3. Stanford
 If USC wins by 7 goals with 12 goals or fewer, then
   the MPSF seeding is
1. Stanford (tiebreaker #2: most goals), 2. USC (head to head), 3. UCLA
 If USC wins by 7 goals with 14 goals or more, then
   the MPSF seeding is 1. USC (tiebreaker #2: most goals), 2. UCLA (head to head),
3. Stanford
 If USC wins by 7 goals with a score of 13-6, then it goes to the third tiebreaker (head-to-head), then
   the MPSF seeding is
1. Stanford, 2. USC, 3. UCLA.
For Stanford to be seeded #1 at MPSF, USC must win either by 6 goals or fewer, or by 7 goals with no more than 13 goals.