* Napoli score twice in last five minutes to defeat Siena
* Lazio must improve to challenge Juve - Petkovic (Adds quotes)
ROME, Dec 22 (Reuters) - Lazio moved up to second place in Serie A after a 1-0 win at Sampdoria on Saturday helped them leapfrog Inter Milan, who could only draw 1-1 at home to Genoa.
Hernanes' goal half an hour into a scrappy match with struggling Samp sent Vladimir Petkovic's team up to 36 points, eight behind champions and league leaders Juventus, who won 3-1 against Cagliari on Friday.
"We worked hard for this, in the last month we have started to believe that we can do something important," Lazio coach Vladimir Petkovic told Sky Italia.
But Petkovic said his side still needed to improve if they were to challenge Juventus for the title.
"We are doing better and better, we are more and more convincing, and some players are coming into form. We are doing well, but not well enough to compete with Juve," he said.
Andrea Stramaccioni's Inter dropped to fourth place after Esteban Cambiasso's equaliser five minutes from time cancelled out Ciro Immobile's superb individual goal for second bottom Genoa.
The result left Inter nine points off the top going into the Italian mid-season break.
"Today the result wasn't positive but I have to compliment the team, we're in a strange period," Stramaccioni said.
"The break is coming at a good time, now we're going to take our minds off things and come back stronger... Things are right for a good 2013."
FIORENTINA GO THIRD
Two Stevan Jovetic goals either side of halftime and a second penalty from Gonzalo Rodriguez were enough for Fiorentina to win 3-0 at troubled Palermo.
Vincenzo Montella's dark horses moved above Inter into third, on the same points as the Nerazzurri and one behind Lazio.
Napoli, who were docked two points in midweek for the involvement of their players in a betting and match-fixing scandal from 2010, scored two goals in the last five minutes in a dramatic 2-0 win at bottom club Siena.
Christian Maggio netted before Edinson Cavani converted from the spot.
Walter Mazzarri's side were far from their thrilling best but stay in fifth and within two points of Lazio, putting pressure on the other challengers for the Champions League places.
German Denis' 40th-minute penalty, his seventh goal of the season for Atalanta, helped the hosts draw 1-1 with Udinese, who had taken the lead seven minutes previously through Luis Muriel's first of the campaign.
Torino comfortably saw off Chievo 2-0 in Turin while Frederik Sorensen's goal for Bologna nine minutes into the second half was cancelled out by Jaime Valdes two minutes later before Nicola Sansone netted on 66 minutes to give Parma a 2-1 away win.
The weekend's big game takes place at the Stadio Olimpico in Rome later (1945 GMT), where flamboyant AS Roma take on a resurgent AC Milan led by red-hot striker Stephan El Shaarawy.
Serie A then stops for a mid-season break until Jan. 5. (Writing by Terry Daley; Editing by Mark Meadows and Stephen Eisenhammer; email@example.com; +44 20 7542 7933; Reuters Messaging:; firstname.lastname@example.org)
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- Vladimir Petkovic