With two outs in the 10th, Alonso hit a 3-2 pitch from reliever Dustin Richardson to the opposite field, just inside the left field foul pole. The 21-year-old first baseman also hit an RBI double in the sixth and raised his average to .327 in 30 Hawaii Winter Baseball contests.
Giants first-rounder Buster Posey went 2-for-5 with a run scored and Alex Garabedian (Dodgers) hit an RBI single for the BeachBoys (18-16), who moved 1 1/2 games ahead of second-place Honolulu with two to play.
Astros prospect Jordan Parraz was 2-for-4 with his first fall homer and Kyu Hyun Moon also went deep for the Honu (14-19).
Jeremy Papelbon (Cubs) pitched a perfect 10th for the win. North Shore starter Jason Godin allowed two hits and two walks while striking out four over 4 2/3 scoreless innings. The Royals farmhand has fanned 36 and walked 15 in 31 1/3 innings in Hawaii.
Richardson (0-2) retired five batters and was charged with a run on one hit.
Waikiki starter Andrew Brackman (Yankees) yielded two runs on four hits and five walks while striking out three in five innings.
Steve Conley is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.