Second-half strikes by Richard Logan, Ben Smith and Lee Elam sent the home side back to the bottom of the Conference.
Terras boss Garry Hill was sent from the stands and midfielder Dean Howell was given his marching orders ten minutes from time for two bookable offences, but they were the only blemishes on an otherwise perfect night for the travelling supporters.
The margin of victory looked unlikely for the first 45 minutes as Crawley looked the more dangerous side.
Striker Jake Edwards almost put them ahead on 19 minutes with a turn and shot which flashed into the side-netting with keeper Arran Lee-Barrett well beaten.
The Reds went close again on the half hour when young full-back Jamie Lovegrove blasted over from the edge of the box.
Lively winger Tony Scully was the biggest threat for the home side and twice should have broken the deadlock before the interval. The former QPR man stung the palms of the visiting keeper with a vicious angled drive on 36 minutes.
He then, with only Lee-Barrett to beat, scuffed just wide with his less favoured left foot after cutting inside full-back Abdou Elkholti.
Weymouth were almost handed an undeserved advantage at the break when home keeper Ben Hamer missed the ball completely as he tried to catch a corner. The ball landed to the feet of the defender Simon Downer and his volley was cleared off the line by the covering Scott Hiley.
Crawley were forced to make a change for the second half with Pat Sappleton replacing the injured Ben Judge in the centre of defence. And it was the substitute's mistake which gave the Terras the chance to go ahead four minutes after the restart.
He attempted to dive and head the ball in the six-yard box as it bounced two foot off the ground from Elam's cross and got it caught under his body. Raphael Nade stole in to lay the ball back for Logan to slot under the advancing Hamer.
The home side's response was positive and they went close to levelling six minutes later, when Dave Woozley sent a header wide from a free-kick by substitute Lee Blackburn.
Weymouth's slender lead was seemingly not enough to please their boss as he was told to sit in the stands on the hour for abusing the fourth official.
His mood would have improved on 68 minutes, however when his side struck again with a brilliant opportunist strike. A corner by Shaun Wilkinson was nodded down by Nade and captain Smith back-heeled into the top corner from close range.
Crawley went for broke for the last 20 minutes, bringing on striker Ben Strevens for Lovegrove to play in a three-man attack.
They were then given a glimmer of hope when Howell received a second yellow card, but they failed to take advantage and Weymouth killed the game off with nine minutes remaining.
Former Reds player Elam, who had earlier missed a golden opportunity, made no mistake with a superb finish after surging into the box off the right flank.
Terras boss Garry Hill was sent from the stands and midfielder Dean Howell was given his marching orders ten minutes from time for two bookable offences, but they were the only blemishes on an otherwise perfect night for the travelling supporters.
The margin of victory looked unlikely for the first 45 minutes as Crawley looked the more dangerous side.
Striker Jake Edwards almost put them ahead on 19 minutes with a turn and shot which flashed into the side-netting with keeper Arran Lee-Barrett well beaten.
The Reds went close again on the half hour when young full-back Jamie Lovegrove blasted over from the edge of the box.
Lively winger Tony Scully was the biggest threat for the home side and twice should have broken the deadlock before the interval. The former QPR man stung the palms of the visiting keeper with a vicious angled drive on 36 minutes.
He then, with only Lee-Barrett to beat, scuffed just wide with his less favoured left foot after cutting inside full-back Abdou Elkholti.
Weymouth were almost handed an undeserved advantage at the break when home keeper Ben Hamer missed the ball completely as he tried to catch a corner. The ball landed to the feet of the defender Simon Downer and his volley was cleared off the line by the covering Scott Hiley.
Crawley were forced to make a change for the second half with Pat Sappleton replacing the injured Ben Judge in the centre of defence. And it was the substitute's mistake which gave the Terras the chance to go ahead four minutes after the restart.
He attempted to dive and head the ball in the six-yard box as it bounced two foot off the ground from Elam's cross and got it caught under his body. Raphael Nade stole in to lay the ball back for Logan to slot under the advancing Hamer.
The home side's response was positive and they went close to levelling six minutes later, when Dave Woozley sent a header wide from a free-kick by substitute Lee Blackburn.
Weymouth's slender lead was seemingly not enough to please their boss as he was told to sit in the stands on the hour for abusing the fourth official.
His mood would have improved on 68 minutes, however when his side struck again with a brilliant opportunist strike. A corner by Shaun Wilkinson was nodded down by Nade and captain Smith back-heeled into the top corner from close range.
Crawley went for broke for the last 20 minutes, bringing on striker Ben Strevens for Lovegrove to play in a three-man attack.
They were then given a glimmer of hope when Howell received a second yellow card, but they failed to take advantage and Weymouth killed the game off with nine minutes remaining.
Former Reds player Elam, who had earlier missed a golden opportunity, made no mistake with a superb finish after surging into the box off the right flank.