Antonio Di Natale was once again Udinese's hero with the only goal of the game in the 19th minute, getting the home team right in the frame for a place in Europa next term.
Only an inferior head-to-head record after a 3-0 defeat to Lazio in the capital kept them below Saturday's opponent with five games of the season remaining.
Lazio had two good early chances to catch Udinese cold, but Zeljko Brkic was alert to thwart the first threat from Antonio Candreva before Miroslav Klose arrived just too late to meet Candreva's cross in the third minute.
Brkic then made a save low down to prevent Cristian Ledesma from opening the scoring during a bright opening from the visitors.
Medhi Benatia was next up to prevent Klose from getting a sight of goal before Gabriel Silva cut in to prevent the German's through ball from reaching Marius Stankevicius as Udinese continued to struggle to get out of their own half.
When they did, they knew they could rely on Di Natale, who did not let them down in the 19th minute.
Silva exchanged passes with Robert Pereyra before crossing the ball for Di Natale, whose acrobatic effort brought the Stadio Friuli crowd to their feet.
It was a punctuation of Lazio's dominance, which continued straight afterwards with Stefano Mauri's deflected effort hitting the post and Brkic denying Ledesma on the rebound.
The Biancoceleste maintained the pressure after the break, although the better chances fell at the other end when Udinese launched their counter-attacks.
On the hour mark, Dusan Basta was presented with the chance to double their lead by Andre Dias. But, with the goal at his mercy and Federico Marchetti stranded off his line, he failed to hit the target.
Marchetti then denied Piotr Zielinski before Di Natale sent a shot wide of the post from the Polish forward's assist.
As Lazio continued to search for a route back into the game, Di Natale went close again to making it 2-0, but his first touch let him down and allowed Michael Ciani to get in a saving tackle.