The Frederick Keys exploded for five runs in the seventh inning last night and defeated the Prince William Cannons, 8-4, in a Carolina League game in front of 3,953 at Prince William County Stadium.

The Keys, second in the league in offense, had been kept in check at the plate by left hander Gerald Nielsen, who used a good curve ball and an effective changeup to limit Frederick to two runs on six hits through six innings.

But Dan Berthel led off the seventh with a single to center and Tony Beasley sandwiched an RBI double between two outs.

Then the Northern Division-leading Keys rapped five straight hits, including a three-run home run by Tim Holland, off Nielsen and left-handed reliever Art Canestro to take a 7-1 lead.

"Our team had been in an offensive slump for too long," said Frederick Manager Wally Moon. "But I felt good about the way they were swinging the bats tonight. Hopefully we're out of it."

Prince William answered with three runs in the bottom half of the inning. J.T. Snow and Sherman Obando opened with consecutive singles and Russ Davis, who hit a solo home run in the fifth inning, followed with a double off the centerfield wall that scored both base runners. An RBI single by Dave Howell chased starter Chuck Ricci, and Steve Mondile came on to squelch the rally.