The game looked to be heading towards a goalless draw before the Bianconeri’s captain Antonio Di Natale struck to score his 27th goal of the season.
With seconds remaining the home side doubled their lead in contentious circumstances as Roberto Pereyra scored in stoppage time to wrap up all three points.
Udinese charged forward on the counter-attack with Lazio’s goalkeeper Federico Marchetti out of position after he had gone up for a corner.
Lazio’s players stopped, thinking they had heard the full-time whistle, but the whistle came from the crowd - and Udinese’s players continued upfield with substitute Pereyra executing a brilliant finish from distance.
Incensed, the Lazio players and coaching staff rounded on the referee and fourth official, causing ugly scenes, with Andre Dias earning a red card for his part in the melee.
Controversy aside, this win means there are now four teams – Udinese, Internazionale, Lazio and Napoli – on 55 points as they battle to secure a third-place finish in Serie A.
With so much at stake, both sides played tentatively at the Stadio Fruli, with misplaced passing and niggly fouls the themes of the opening 45 minutes.
The few moments of quality were produced by Udinese. A curling free-kick from Di Natale looked destined to ripple the back of the net, until Marchetti flung out his hands to beat the effort away.
Giampiero Pinzi had the Lazio goalkeeper scrambling across his goal when he pulled the trigger from 30 yards, sending a vicious shot inches over the bar.
One of Lazio’s few forays into the home side’s half almost produced a goal on the cusp of half-time. Abdoulay Konko charged down the right win and picked out Tommaso Rocchi with a pinpoint cross and the striker sent it goalwards with a header that was brilliantly turned over by Samir Handanovic.
That was as close to scoring as Lazio came. Udinese continued to dominate possession in the second half, but were reduced to long range efforts by Lazio’s resilient defence.
Kwadwo Asamoah, Dusan Basta and Di Natale all fired warning shots without troubling Marchetti.
But as the game approached the final 20 minutes the deadlock was finally broken as Di Natale peeled off Dias to volley Maurizio Domizzi’s inch perfect cross into the back of the net.
The visitors threw men forward in search of a leveller, but were unable to find the net before the match was put beyond doubt by Pereyra’s controversial goal.