The win puts Cal State L.A. (46-16-1) into the semifinals against Columbus (50-18) at 12:30 p.m. today.
On Sunday, the Golden Eagles battled back to notch a 4-1 victory against Kutztown.
It was sixth time since it entered the NCAA playoffs that Cal State L.A. has avoided elimination.
Diaz and Williams didn't see any playing time in the three games.
Against Kutztown, Matt Winkleman slugged a two-out home run in the seventh inning to break a scoreless tie to carry the Golden Eagles in the first elimination game of the tournament.
The Golden Eagles added two more runs in the ninth inning. Jeff Carroll opened the inning with a double and scored on Brian Hernandez's single. Kurt Crowell doubled off reliever Phillip Rummell for the final run.
Kyle Owsley (7-3) pitched a fine game for the Golden Eagles, tossing seven scoreless innings. Arturo Reyes pitched the final two innings to post his 10th save.
Cal State L.A. opened the tournament Friday with a 13-5 loss to defending champion Tampa.
The Spartans (50-10) scored four runs in the first, three in the fourth and five in the seventh to walk away with the win.
Cal State L.A. came back to make the score 8-5 by scoring single runs in the middle three innings. But Tampa's five-run seventh closed the door on the Golden Eagles' rally.
Fernando Franco and Crowell each had two hits for the Golden Eagles.
Two weeks ago, the Golden Eagles lost to Chico State in their opening game of the NCAA West Regional and then posted wins over Nebraska-Kearney, Sonoma State and Mesa State (twice).