A constant threat from set pieces themselves, the home side levelled in the 36th minute through Joan Edmundsson, who stabbed home Ragnar Nattestad's pull-back after a long throw-in caused panic in the Irish defence.
Booked early in the first half, Edmundsson saw red following a late challenge in the 65th minute.
Six minutes later McCauley put his side in front again, holding off his marker to head home, and Lafferty put the game out of reach when he swivelled to rifle home a shot four minutes later.
The win takes Northern Ireland to 16 points, one ahead of Romania following their goalless draw away to Hungary, who have 12.
Northern Ireland are at home to Hungary on Monday when a win would guarantee them a top two spot and a place in next year's finals in France.
(Reporting by Philip O'Connor, editing by Mitch Phillips)
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