The Nerazzurri's poor home form continued as Francesco Guidolin's Scudetto-chasers emerged winners in a thrilling game, which saw two penalties and two red cards
Damiano Feronetti received his marching orders late in the game after he brought down Diego Milito in the box, but Giampaolo Pazzini also missed from the spot as both teams finished with ten men and a spurned penalty each.
Inter were the better team in the early minutes of the game as they were superbly shutting out Udinese's midfield and attack. Milito was the first to seriously threaten Samir Handanovic's goal as in the eighth minute but the Argentine sent a volley well over the bar from a difficult angle.
'El Principe' was guilty of another miss later on, when a through ball by Zanetti found the striker in space inside the penalty area, but he once again failed to find the target. Udinese, however, started to wake up from their lethargic start and soon began creating chance of their own.
In the 22nd minute, a good pass by Antonio Di Natale found Isla free in the box, but the Chilean could only strike wide with just Julio Cesar to beat. Inter were struggling to repel Udinese's attacks, which were growing more dangerous by the second.
The visitors' over-eager play, however, was leaving them vulnerable at the back, and on the half-hour mark Thiago Motta nearly put the Nerazzurri in front after a delightful one-two with Milito.
The two teams continued to trade chances in the second half as shortly after Gabriel Toje had a header saved in the 54th minute, Pazzini missed a similar opportunity on the other side of the pitch.
Still, Udinese's abundance of pace was causing Inter problems and the visitors were finally rewarded for their efforts. In the 73rd minute, a quick break saw Antonio Floro Flores rush between Walter Samuel and Andrea Ranocchia before teeing up for Isla on the right side of the box, and the Chilean made no mistakes with his thunderous finish.
Inter tried to mount a late comeback, but often found themselves exposed on the counter. One such break saw Zanetti foul Kwadwo Asamoah in the box, which resulted in a penalty for Udinese and a second yellow card for the captain. Di Natale, however, saw his spot-kick kept out by Julio Cesar.
Just as things looked hopeless for the Nerazzurri, Feronetti brought down Milito in the box in a moment of madness, which earned him two bookings in two minutes. The drama was completed, when Pazzini skied his penalty over the bar, wasting a chance to earn a point for his team.
This result sees Udinese draw level on 27 points with leaders AC Milan, while Inter sit 15th, four points above the relegation zone but could drop further down after Sunday's round of matches.