Tony Williams added to that in the 10th minute when he pounced on a Trent Hodkinson kick tapped back by Chase Stanley.
Lafai then scored the first of his tries in the 25th minute as Sam Kasiano created some second phase play.
He then chased down his own grubber eight minutes later to touch down, before adding his third four minutes after halftime as he made his way through some poor Dragons defence out wide.
Greg Eastwood then charged over to put the Dogs up 32-0 after 61 minutes, before Josh Reynolds raced 92m to score an intercept try in the 69th minute for a 38-0 scoreline.
Brett Morris chased down a Widdop kick in the 77th minute for a consolation offering for the home side.
After another below par effort from the Dragons, who have won just one of their last six games, Benji Marshall could be rushed straight back into Steve Price's lineup for their round 10 match against Parramatta on Saturday.
- AAP