Pieson went the first four innings struck out five, scattered four hits, and won her 17th game of the season, with three losses.
Navarrete and Molina combined to pitch three perfect innings in relief.
Mt. SAC, ranked first in the state, improved to 26-3 on the season with its ninth win in a row and 13th in the last 14 games.
Leading the team in hitting were catcher Annemarie Gutierrez (3 for 3, 2 RBIs) and first baseman Brianna Goris (2 for 3, R). Goris is first in the state with a .582 average (46 for 79) and tied for the lead with 11 home runs.
Gutierrez's two-run single to right-center, scoring Goris and second baseman Asia Chacon gave the Mounties all the runs they needed.
That was followed by solo home runs by Diaz and Barcelona in the second for the 4-0 lead.
The home runs by the two sophomores were the 26th and 27th of the season by the Mounties, which were second in the state only to San Mateo with 31.
Barcelona scored the fifth run of the game for the Mounties in the fourth inning for the 5-0 lead.
Mt. SAC takes on Rio Hondo on Tuesday (April 5) for a South Coast Conference game.
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For additional information, please contact the Mt. SAC Sports Information Office at 909.274.4630.