Lazio beat Roma 3-2 in a rain-drenched derby match in Serie A on Sunday, which saw both teams reduced to 10 men.
Inter Milan's 10-game winning run in all competitions, meanwhile, was snapped with a surprise 3-2 loss at Atalanta.
After ending Juventus' 49-game unbeaten run in Serie A last weekend, Inter has slipped four points behind the leader and defending champion. It is also only a point ahead of Napoli, which beat Genoa 4-2.
A defensive howler from Roma right back Ivan Piris allowed Mauri to make it 3-1 to Lazio.
In a dramatic finale, Mauri was sent off for a second booking before substitute Miralem Pjanic pulled one back for Roma. However, Lazio clung on for its third successive derby victory.
Elsewhere, AC Milan missed a penalty in losing 3-1 against Fiorentina.
In Rome, there were tributes before the match to Gabriele Sandri, the Lazio fan killed by a stray police bullet five years ago. Tensions were high and a Roma fan was stabbed outside the stadium before kickoff as trouble threatened to flare, with objects -- including a Molotov cocktail -- thrown across the heavy police cordon separating the rival fans.
On the pitch, play had to be halted for a few minutes as the floodlights failed.
Lazio leveled in the 35th with a stunning long-range free-kick from Candreva which slipped through Goicoechea's hands.
Klose gave Lazio the lead three minutes from halftime as he slotted in Hernanes' through ball.
Matters got worse for Roma minutes later as De Rossi became the 13th player to be sent off in nine matches between the two.
"I'm disappointed with De Rossi's actions," Roma coach Zdenek Zeman said. "We talked for two days about those risks, that you didn't need to react or give in to provocation. Of course emotions are high in the derby, but when you feel it too much you pay.
"I haven't talked to De Rossi yet. He went to jump, was held back and reacted that way. What else is there to add? I'm disappointed for him and the team. We'll have to play the next games without him."
Lazio extended its lead immediately after the break as Roma's Piris headed an innocuous-looking long ball straight to Mauri on the edge of the area and the Lazio striker smashed it in.
Lazio seemed to be heading for a comfortable victory before Mauri was shown a second yellow for handball. Pjanic scored moments later with a free-kick from 30 meters after spotting Lazio goalkeeper Federico Marchetti off his line.
Roma almost leveled deep in stoppage time after a fantastic pass from Michael Bradley which Pablo Osvaldo fired wide.
Inter had won all its away games this season ions but was stunned in the ninth minute when Giacomo Bonaventura headed in Federico Peluso's cross.
Atalanta goalkeeper Andrea Consigli was in fine form to deny Inter time and time again, and Atalanta should have doubled its lead when German Denis astonishingly hoofed the ball over the bar from five meters out in front of an open goal.
Inter was level when Fredy Guarin fired in a missile of a free kick, but Denis put Atalanta back in front in the 60th and then extended its lead seven minutes later, sending Samir Handanovic the wrong way with a penalty after Matias Silvestre appeared to have been harshly judged to have brought down Maxi Moralez.
Handanovic pulled off a stunning save to deny Facundo Parra before Rodrigo Palacio pulled back a consolation goal late on.
Parra was somewhat harshly shown a red card in stoppage time for a shove on Guarin.
Milan was jeered off the pitch at halftime and fulltime after losing at home to Fiorentina.
Former Milan midfielder Alberto Aquilani gave Fiorentina the lead in the 10th minute but the home side should have leveled from the penalty spot after Alexandre Pato was bundled over by Facundo Roncaglia.
However, Pato blazed his spot kick way over the crossbar.
Mexes redeemed himself somewhat on the hour mark with a backheel which bounced off the right post and straight to substitute Giampaolo Pazzini for an easy tap-in for the former Fiorentina star.
There were fears Napoli's game would not go ahead with Genoa on lockdown amid flood warnings, following knock on effects from Hurricane Sandy.
However, the game went ahead and Genoa — which had lost all three games under Luigi Del Neri — stunned Napoli by taking the lead through Ciro Immobile.
In the lunchtime fixture, Palermo beat fellow strugglers Sampdoria 2-0 with teenager Paulo Dybala notching his first goals in Serie A.
The 18-year-old forward was given a standing ovation when he was substituted in stoppage time.
The loss is Sampdoria's seventh successive defeat and could spell the end for coach Ciro Ferrara's brief time in charge.
Elsewhere, Gabriele Angella scored twice to help Udinese draw 2-2 at Chievo Verona. The defender also had a goal wrongly disallowed for offside.
Chievo's Luciano had thumped an earlier penalty off the crossbar. Danilo was sent off late on after receiving two yellow cards for giving away both penalties.
Torino picked up its first victory in six games with a 1-0 win over Bologna, while Parma drew 0-0 at home to Siena.
Information and The Associated Press was used in this report.