Ulloa, who has now scored eight goals in 11 English games, broke the deadlock on 43 minutes, when he headed home from close range after a brilliant jinking run and cross from the right by William Buckley.
© PA Photos
Buckley was at the centre of the action again moments later, as the former Watford winger was chopped down just outside the penalty area by Kagisho Dikgacoi.
Dikgacoi was issued with a yellow card, but he was then punished further as Lopez curled the resultant dead ball into the back of the net via the underside of the crossbar.
© Gareth Fuller / PA Photos
Palace and Brighton remain fourth and seventh respectively in the Championship table.