Will Buckley scored both goals for the visitors as Brighton claimed victory at London Road this evening.
The winger snatched all three points with a low drive from the edge of the area two minutes from time to extend the Seagulls' unbeaten run to five games.
After a stale opening it was Gus Poyet's men who began to impose themselves, with Matt Sparrow firing wide midway through the half.
Buckley put Brighton one up with a long range free kick which, with the assistance of the gusty wind, dipped over Joe Lewis in Peterborough's goal.
David Ball levelled for the home side, who rarely fail to find the net in front of their own fans, by turning home Ryan Tunnicliffe's front-post centre.
Both sides went for the win in the dying moments but it was Albion who secured the win with Buckley's fizzed effort.
Despite the loss, Darren Ferguson's men remain 16th while Brighton jump two places to tenth.
