The Trawlerboys moved up one place to fourth, above Canvey, and narrowed the gap on leaders Whitehawk to 11 points with four games in hand.
Defty (pictured) opened the scoring after 10 minutes and defender Erkan Okay added his first goal of the season midway through the half.
Another strike by Defty on the hour took his tally to 17 and made it 3-0, leaving the Met the consolation of a late reply by Dave Knight.
Second-placed Wealdstone could only manage a 0-0 draw at lowly Thurrock. They are six points off the pace, now with only one game in hand.
Leatherhead and Folkestone, occupying fifth and sixth places in Ryman South, were separated only by goal difference when they kicked off at Fetcham Grove.
And there was to be nothing between them on the night. Tom Bradbrook put the hosts ahead in the 61st minute but Folkestone replied through Phil Stevenson 14 minutes later.
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