Teenager Evan Ferguson scored twice to send Brighton through to their third FA Cup semi-final and bring Grimsby Town's dream run to an end at the Amex Stadium.
Deniz Undav put the hosts in front after six minutes, following in to slot past Max Crocombe after the visiting goalkeeper had parried Moises Caicedo's shot.
Without being at their best, Roberto de Zerbi's side controlled the game throughout and Ferguson added a superb second fives minutes into the second half.
The 18-year-old striker stretched to bring down Alexis Mac Allister's clipped pass with his left foot, set himself and then stroked the ball into the bottom corner.
Ferguson burst through to score his second on 70 minutes, Solly March made it four with a diving header and Kaoru Mitoma's deflected 90th-minute strike crept in at the near post to complete the scoring.
Grimsby had knocked out five teams from divisions above them to reach their first FA Cup quarter-final for 84 years but for all their defensive discipline in the first half, the League Two side's attacking threat was extremely limited.
Brighton keeper Robert Sanchez nearly gave them a way into the game when he appeared to pick the ball up outside his area under pressure, but a VAR check concluded that the ball was just on the line when he did so.
Substitute John McAtee had Grimsby's two chances of note, trying to lift the first over Sanchez and seeing the second pushed around the post by the Spaniard in the closing stages.
While the margin of victory could have been greater, with Mitoma missing a gilt-edged chance and Adam Webster hitting the bar, the Seagulls can now look forward to a trip to Wembley and a first semi-final since 2019.
More must-reads: