Former European Cup winners Red Star missed a chance to gain ground on Partizan, who are chasing a record sixth successive league title, after they slumped to a 3-0 home defeat by Vojvodina Novi Sad in the evening kickoff and piled the pressure on their coach, Aleksandar Jankovic.
The results left Partizan top on 37 points from 15 matches, followed by Red Star on 31, Jagodina on 29 and Vojvodina on 28 points.
Cool finishing by forwards Lazar Markovic and Marko Scepovic in each half gave Partizan a 2-0 lead on a sunny afternoon in northern Serbia but late defensive blunders on a bumpy pitch cost them and infuriated coach Vladimir Vermezovic.
Substitute Aleksandar Noskovic pulled one back after Partizan defender Milos Ostojic was caught out of position and 36-year-old centre back Vidak Bratic headed home a free kick in the dying minutes after slack marking by his Bulgarian counterpart Ivan Ivanov.
"I warned the players at halftime to watch out for set pieces and I yelled so much before the free kick to make my players pay attention, but it seems everyone in the stadium except them heard me," Vermezovic told a news conference.
"But that's football and we got punished for not taking our chances in the first half so we can't complain."
Red Star, who won Europe's premier club competition in 1991, were undone by their former player Aboubakar Oumarou, who scored a first-half brace before midfielder Miroslav Stevanovic sealed Vojvodina's win shortly after the interval.
The Cameroonian striker nodded in the opener after a goalmouth scramble but there was nothing opportunist about his second, when he raced past three markers from the halfway line and beat keeper Boban Bajkovic with a crisp low shot from 15 metres.
Visiting fans celebrated the third by lighting flares after Stevanovic turned in a corner from close range and Red Star fans treated their team to a chorus of jeers after the final whistle.
The league resumes on Feb. 27, when Partizan are away to neighbours BSK Borca while Red Star entertain Javor Ivanjica.