* Fiorentina, Inter also lose
* Stoppage-time goal pushes Palermo into more trouble
MILAN, Jan 6 (Reuters) - Teenage Argentine Mauro Icardi scored twice as Serie A leaders Juventus slumped to a 2-1 defeat at home to lowly Sampdoria who came from behind to win despite playing for an hour with 10 men on Sunday.
Juve had won their last four Serie A games while Sampdoria had lost 10 of their last 13 and only one outcome looked possible after Sebastian Giovinco put the hosts ahead with a 24th-minute penalty and Sampdoria had Gaetano Berardi dismissed.
Instead, Icardi netted twice in the second half as Sampdoria hit back out of the blue.
There was a further shock as third-placed Fiorentina went down to their first home defeat of the season, losing 2-0 to relegation-threatened Pescara, and fourth-placed Inter Milan were beaten 3-0 at Udinese as they continued their slump.
Goalkeeper Mattia Perin was the hero for Pescara, saving everything Fiorentina could throw at him before Jonathas and Mervain Celik snatched the points by scoring from the visitors' only two real chances.
Inter dominated the first hour at Udinese and missed a flurry of chances including one incredible effort from Brazilian Jonathan who contrived to fire wide from six metres in the 54th minute with the goal at his mercy.
They paid the price when 35-year-old striker Antonio Di Natale scored twice and Colombian Luis Muriel was also on target in the closing half hour.
Inter's unhappy afternoon was complete when defender Juan Jesus sent off for a second bookable offence.
Juventus, with 44 points from 19 games, still reached the halfway mark in the championship with a five-point lead over Lazio, who beat Cagliari 2-1 on Saturday. Fiorentina and Inter have 35 points.
In other matches, two goals by Marco Boriello gave Genoa a 2-0 win over Bologna which lifted them out of the relegation zone while Bojan Krkic and Giampaolo Pazzini scored to give seventh-placed AC Milan a 2-1 win at home to bottom club Siena.
Chievo Verona beat Atalanta 1-0 in a midtable clash and a stoppage-time goal from Amauri gave Parma a 2-1 win over Palermo which left the Sicilians one place off the bottom with 15 points, one below Cagliari and two adrift of 17th-placed Genoa.
Igor Budan had put Palermo level in the 85th minute, wiping out Ishak Belfodil's opening goal.
Juventus had won 14 of their first 18 games and took the lead when Giovinco converted a penalty awarded after Claudio Marchisio was fouled in the 24th minute.
Seven minutes later, Berardi was given a second yellow card as Sampdoria's problems multiplied.
But Sampdoria levelled seven minutes after the re-start when Juventus goalkeeper Gianluigi Buffon misjudged Icardi's awkwardly bouncing shot.
In the 68th minute, the 19-year-old got to the byline and then fired into the roof of the net from an almost impossible angle.
Fiorentina should have been several goals clear at halftime against Pescara but Perin brilliantly kept the hosts at bay with saves from Alberto Aquilani, twice, and Borja Valero.
Jonathas then headed the visitors in front after 57 minutes and, despite further Fiorentina pressure, Celik added another in stoppage time when he won the ball off Sebastian Rocaglia and slid his finish under goalkeeper Neto. (Writing by Brian Homewood in Berne; Editing by Toby Davis)