Udinese joined AC Milan at the top of Serie A after a 1-0 win at Inter Milan on Saturday ensured that the hosts remain stuck in a relegation dog-fight.
Mauricio Isla scored the only goal to draw Udinese level on points with Milan, who lead on goal difference after their 2-0 win at Genoa on Friday.
Third-placed Juventus, who are a point behind, can reclaim the lead if they beat second-from-bottom Cesena at home on Sunday.
But while unfancied Udinese were celebrating the continuation of their stunning start to the season, giants Inter continue to struggle and remain 15th, although they could yet drop lower before the weekend is out.
In a crazy finish two penalties were missed in the last four mintues, one at each end, with a player also being sent off for each side.
"Logically we wanted a different result but we pushed, we tried to put them in difficulty," said Inter coach Claudio Ranieri.
"Sometimes we managed but they're good, they leave you to attack, they wait and then counter very well. Well done to Udinese. Tomorrow we'll try to be positive and think about what we need to do."
Udinese coach Francesco Guidolin said: "The first half was even although maybe Inter had a bit more of the game but in the second we did so many good things.
"Udinese don't often win at the San Siro, we're (joint) top at the moment, that's fantastic. We'll enjoy the present and we'll see what happens in the future."
The first half was a turgid affair with little in terms of goalmouth action but after the break Udinese proved far the more effective.
Captain and emblematic striker Antonio Di Natale almost caught out goalkeeper Julio Cesar with a surprise snapshot on the turn.
Isla and Di Natale then broke clear of the Inter back line but wasted the chance before the latter was wrongly ruled offside anyway.
But they found the breakthrough 17 minutes from time as Pablo Armero released Di Natale who fed substitute Antonio Floro Flores to tee up Isla to fire home.
Di Natale could have made the game safe four minutes from time after Inter captain Javier Zanetti conceded a penalty for a foul on Kwadwo Asamoah that earned him a second yellow card, but Julio Cesar saved the striker's spot-kick.
Inter were awarded a penalty a minute from time when Damiano Ferronetti was adjudged to have brought down Diego Milito but Giampaolo Pazzini slipped as he struck the spot-kick and sent the ball flying over.
Ferronetti, who was booked for the foul, then continued to protest to the referee and was shown a second yellow, meaning both teams finished with 10 men.
Napoli earned their first win in five league games to reignite their title hopes as they strolled to a 4-2 win over rock-bottom Lecce.
It was just the type of game Napoli coach Walter Mazzarri, who rested several first-choice players, was looking for ahead of the southerners' trip to Villarreal in midweek, when they may need to win to progress to the Champions League knockout rounds.
Ezequiel Lavezzi opened the scoring on 26 minutes with an individual goal, weaving infield from the left and skipping past three players before beating Lecce goalkeeper Massimiliano Benassi.
The second came just past the half-hour mark after Goran Pandev, who may have played himself into the starting line-up on Wednesday night, sent a brilliant defence-splitting pass to Edinson Cavani, who easily beat Benassi.
The third came just before the break as Lecce failed to clear their lines and Blerim Dzemaili fired home through a crowd of players from 25 yards.
Luis Muriel and Daniele Corvia scored for Lecce in the second half while Cavani added his second for Napoli.