Diouf stepped up to coolly convert from 12 yards after Adam El-Abd handled with 10 minutes remaining at the Keepmoat Stadium.
Brighton led at the interval through Craig Mackail Smith, but Gus Poyet's play-off chasers were forced to defend for long periods against the division's bottom club.
Birmingham's draw with Derby means the Seagulls remain a point outside the top six.
Meanwhile, Dean Saunders' Rovers are six points from safety with two games in hand on fourth bottom Bristol City ahead of Tuesday's vital trip to Nottingham Forest.
James Coppinger returned to the Doncaster line-up following six weeks on the sidelines with a broken cheekbone as Carl Ikeme started in goal after rejoining on loan from Wolves and James Hayter was preferred to Kyle Bennett in attack.
Poyet named a Brighton side unchanged from last weekend's impressive 3-0 win over Ipswich.
Blustery conditions and a ragged playing surface made for a scrappy opening, during which home captain Brian Stock hobbled from the field to be replaced by Simon Gillett.
Matters were made worse for Stock's team-mates in the 20th minute when Brighton took advantage of a statuesque Rovers defence to take the lead.
Liam Bridcutt heavily scuffed a 20-yard effort, but Mackail-Smith was alive to the possibilities and managed to poke past Ikeme at the second attempt.
The goalscorer almost gave Doncaster an immediate route back into the game as he received a yellow card for a foul on Pascal Chimbonda and Giles Barnes headed over from the resulting free-kick.
Gillett was doing his best to provide ammunition for the Rovers forwards, with Mamadou Bagayoko forcing a save from Peter Brezovan via an audacious backheel from the former Southampton midfielder's cross.
In the 44th minute James Hayter blazed over from inside the area after Gillett's shot was blocked, while at the other end Will Buckley almost gave Brighton a scarcely-deserved second on the break when he fired into the side netting.
Doncaster remained on top at the start of the second period got under way, as Coppinger smashed a volley narrowly past the post.
El-Hadji Diouf and Chimbonda then combined effectively down the right wing for the latter to cause panic in the Brighton penalty area with a low cross. The ball eventually found Rovers full-back Tommy Spurr, whose drilled effort was deflected wide.
The hosts remained on the front foot, but Albion were starting to enjoy opportunities on the break as Mackail-Smith narrowly failed to get his head to a dangerous centre from substitute Craig Noone.
As Doncaster's efforts took on an air of desperation they were handed a lifeline when Adam El-Abd inexplicably handled a Diouf corner, allowing the Senegal international to nonchalantly slot home from the spot.
Both managers sent on playmaking substitutes and Brighton's Gai Assulin and Doncaster's Fabien Robert might have snatched victory for their respective sides before the points were shared.