Mason County (Maysville, Ky.), a Kentucky state semifinalist last season, withstood nine 3-pointers and a second-half rally by Kaimuki yesterday to win, 50-46, in the opening round of the 28th Annual 'Iolani Prep Classic.

The Royals, who return three starters from a team that went 25-7 and won its fourth straight region championship, advance to tonight's 8 o'clock semifinal against Mount Vernon (N.Y.), which is ranked No. 14 in the USA Today Super 25.

Mason County led 11-3 after the first period and 24-14 at the half, but closed it to 32-28 by the end of the third quarter. The Bulldogs, who are 3-2 in the O'ahu Interscholastic Association after back-to-back three-point victories, had possession with under a minute remaining but failed to convert.

Tyler Black led the Royals with 16 points, and Southern Illinois recruit Treg Setty and Jordan Gilbert each added 14 points.

Mason Kuali'i-Moe, who drained four 3-pointers, and Tevin Nishiyama, who sank two from beyond the arc, each scored 14 points to lead Kaimuki. Dio Taulung added 13 pointers, including three 3-pointers.