Michael Gilchrist contributed 12 points, eight rebounds and three blocked shots as top-seeded St. Patrick, No. 1 in The Star-Ledger Top 20, dealt an 82-45 setback to second-seeded and No. 5-ranked Plainfield yesterday at Kean University’s Harwood Arena in Union. The margin of victory was the largest in a championship game in the history of the 74-year-old tournament and the contest was not as close as the score might indicate. And this was against the fifth-ranked team in the state, whose only prior losses were to St. Patrick and to No. 3 St. Anthony.