Albion's battle to beat the drop suffered a blow with a disappointing first home defeat for six games.
Goals in the last 19 minutes by Michael Jackson and Richard Cresswell kept the Seagulls in the bottom three.
The only consolation for Steve Coppell's side was that fellow strugglers Stoke and Grimsby also lost.
A frustrated crowd of 6,669 at Withdean saw centre-half Jackson break the deadlock on 71 minutes with a powerful header from a Graham Alexander corner.
It was a sloppy way for Albion's run of four straight clean sheets at home to end.
Ironically, they conceded both Preston goals from corners when the teams drew 2-2 at Deepdale in November.
Cresswell made certain of the points with a fine individual effort on 86 minutes.
The striker celebrated his 100th appearance for the visitors by firing a shot in off a post from the edge of the area after a solo run, his 16th of the season.
Preston boss Craig Brown did not see Cresswell's match-clinching contribution.
The former Scotland coach had been banished to the dressing room by ref. Len Cable for protesting when Pawel Abbott appeared to be blatantly brought down inside the Albion area by keeper Dave Beasant.
The Seagulls were denied by the woodwork twice in quick succession in the first half.
Captain Danny Cullip crashed a close-range drive against a post following a long throw from Kerry Mayo.
Seconds later Bobby Zamora's towering header from a Richard Carpenter corner thumped against the crossbar.
Paul Watson and Simon Rodger also went close in the opening period, but it was a different story after the break as Preston raised their game.
Albion remain third bottom, a point behind Stoke who were beaten 3-1 at Millwall.
Grimsby were hammered 4-1 at home by Crystal Palace and they are now bottom, three points adrift of the Seagulls.
Sheffield Wednesday moved a point above them with a shock 2-1 win at Portsmouth, denying Pompey the victory they needed to clinch promotion.
It looks very much like three from four for the drop as Walsall and Derby eased their relegation worries with wins at Gillingham and Wimbledon respectively.
Albion visit new leaders Leicester next Saturday. Micky Adams' men moved a point above Portsmouth with a 1-1 draw at Rotherham.
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