Rookie Sam Randolph, the 1985 U.S. Amateur champion, won his first PGA golf tournament as rain canceled the scheduled final round of the $500,000 Bank of Boston Classic yesterday in Suffolk.

Only four players in the field of 82 had completed the fourth round when play was suspended in late morning by heavy rain.

Officials at Pleasant Valley Country Club waited for three hours before canceling the round.

Randolph, 23, shot a 7-under-par 64 Saturday, one stroke off the course record, for a 54-hole score of 199, a Pleasant Valley record for three rounds.

Four strokes back were defending champion Gene Sauers, Australian Wayne Grady and Canadian Ray Stewart . . .

Nancy Lopez, who began the day two strokes behind the leader, sank a five-foot putt on the 18th hole to finish at 6-under 210 and win the Ping tournament in Portland, Ore., by one stroke.

Lopez and Jan Stephenson began the 18th hole tied for the lead. Both players hit their approach shots to the right of the green and chipped to within five feet.

Stephenson bogeyed, ending up tied with Kelly Leadbetter and Muffin Spencer-Devlin for second in the $225,000 LPGA tournament.