The Shammies (10-2) and Vikings (9-3) had entered the game tied for top spot.
Gonzaga reliever Tyler Vincent suffered the loss.
Scott Stockley of the Shamrocks and Peter Madden of Gonzaga each had two hits.
In a second senior game at St. Pat’s, the Holy Cross Trinity Pub Crusaders blasted the Fifth Ticket Feildians 14-4 in a game shortened to six innings by virtue of the 10-run mercy rule.
Danny Rice had four hits and four RBIs for Holy Cross (4-8), while Dean Norman added three hits for the winners.
Willie Combden had three hits for Feildians (3-8).
Sean Janes went the distance on the mound for Holy Cross, while Feildians starter Alex Walsh was tagged with the loss.
