Argentinian striker Ulloa scored a 75th-minute winner to keep Brighton in touch with the play-off places and condemn struggling Rovers to a third defeat in five matches. To make matters worse for Doncaster, they had striker Billy Sharp sent off late on.
Doncaster's dreadful away form - they are without a win on the road in the Championship since a 1-0 win at Sheffield Wednesday in September - has been a cause for concern for boss Paul Dickov as his men battle to avoid the drop.
But, despite conceding late on, an otherwise resilient display will no doubt give encouragement to the 41-year-old Scot that his Rovers side can avoid slipping too far down the table.
It was the home side, though, that made the better start with Ulloa heading a Stephen Ward cross wide from 10 yards and David Rodriguez failing to connect to a Solly March cross.
New signing Rodriguez, making his full debut, will have to hit the ground running if Brighton are to sustain a play-off push after striker Ashley Barnes departed for promotion-chasing Burnley last month.
The 27-year-old Spaniard arrived at the Amex on transfer deadline day in a deal from Celta Vigo that runs until the end of the season, and he looked at home in a Seagulls shirt thanks to the strong Iberian influence at the club.
Head coach Oscar Garcia and team-mates Andrea Orlandi and Inigo Calderon will help Rodriguez feel at home on the south coast, and the frontman would have put Brighton ahead had he connected with March's searching cross from the right.
Sharp went closest to breaking the deadlock for the away side 10 minutes into the second half when unmarked inside the box.
The 27-year-old, who penned a loan deal from Southampton last month and scored on his return in a 1-1 draw against Blackpool, sent an unchallenged header agonisingly wide from six yards following a cross by James Coppinger.
Ulloa had a 20-yard curling strike kept out by Sam Johnstone and March's close-range effort was blocked by James Husband as Rovers continued to hold firm.
Dickov's men have been reinvigorated by the arrival of commanding 20-year-old Manchester United goalkeeper Johnstone, who made a bright start to his four-week loan spell at the Keepmoat Stadium with a clean sheet in the midweek draw with Middlesbrough.
Johnstone did well to hold an early volley from midfielder Orlandi before denying Ulloa's clean strike from close range in the 65th minute.
Brighton eventually broke the away side's strong resistance, however, when Ulloa met Ward's pinpoint cross from the left with a firm header to snatch all the points for the Seagulls.
Doncaster's misery was compounded when striker Sharp was shown a straight red card in the 86th minute for violent conduct after he attempted to kick Gordon Greer following a tangle with the Brighton defender.