The win is the Lancers' third in a row as they improve to 3-2 overall, 1-0 PacWest. The 'Lopes drop to 2-3, 0-1.
This was the first of a four-game series between the teams.
"When you play someone eight times, it's going to come down to adjustments," said CBU Head Coach Gary Adcock. "Playing a 40-game conference schedule and against everyone eight times is unique. This is one of 40, and we have a long way to go."
After hitting just one home run in the first four games with Cal State L.A., the Lancer offense erupted for three today. Marnati got things started with a two-run shot to deep right center off GCU starter Brady Wager in the first after Johnson reached on a leadoff error.
Marnati also singled three times, doubled, scored four times and drove in three runs.
"We don't expect Matt to go 5-for-5 every game, but we do expect a two-time all-conference selection to lead us offensively," said Adcock. "To get after Wager in the first inning and capitalize on that error was big. It put pressure on them right from the start."
Johnson put three more on the board in the second with a three-run homer that got caught up in the jet stream and sailed over the left field wall to give the Lancers a 5-0 lead. It was his first home run since May 12, 2010, his sophomore season.
That was more than enough for Patrick Smith (1-1), who allowed just three hits and two runs in six innings. He loaded the bases in the third and gave up both runs on a fielder's choice groundout and a wild pitch, and that was it.
Smith struck out four.
"Patrick started well today, and that was a typical outing for him," said Adcock. "We are anticipating him being at the front end of the rotation and that's the kind of performance we expect from him."
Moore put the game away with a grand slam to deep right field to power the Lancers' five-run sixth. Marnati also added an RBI double in the inning.
The Lancers had 19 hits, their highest hit total since getting 20 last March against San Diego Christian.
Johnson was 2-for-5 with three runs and three RBIs. Moore was 2-for-4 with five RBIs. Daugherty, Bullard and Crowley all had two hits apiece.