Rodriguez Vicente's double earned victory for Brighton, who moved into the Championship play-off places, while Portsmouth remain bottom of the table.
Brighton dominated the second half and defender Joe Mattock crashed a half-volley against the post from six yards.
And with 15 minutes left, Vicente fired home a low free-kick from 20 yards to give the hosts a deserved lead.
The Spaniard doubled their advantage in injury time, firing home from 10 yards following Kazenga LuaLua's pass.
The result sees Brighton, who are unbeaten in 12 games, move up to fifth in the table while beleaguered Portsmouth are now eight points from safety.
The visitors, who were last month deducted 10 points for going into administration, were the first to have an opening but Luke Varney curled narrowly wide of the right-hand post from 25 yards.
Scott Allan then made some room for himself just outside the area before his rasping drive was tipped around the post by Seagulls goalkeeper Peter Brezovan.
On the stroke of half-time, the hosts nearly took the lead as an almighty scramble in Portsmouth's penalty box - created by Alan Navarro's long-range shot - ended with Sam Vokes being denied by Jamie Ashdown from close range.
After the break Mattock's volley struck the post before Pompey cleared their lines to ensure the score remained goalless.
Seagulls manager Gus Poyet then introduced former Spain international Vicente for Noone in an effort to break the deadlock. And the replacement almost had an immediate impact as, after Ashley Barnes's strike was blocked by Tal Ben Haim, Vicente's follow-up was saved by Ashdown.
The 30-year-old was not to be denied though, and his free-kick following David Norris's foul put Brighton well on their way to three points.
Portsmouth did push forward in an attempt to force an equaliser but their failure to test Brezovan was telling and their misery was compounded in injury time. LuaLua picked out Vicente from the left and he made no mistake from close range, although there was a clear handball in the lead-up to the goal.