ROME — A defensive blunder helped decide a heated Rome derby but many fans weren't there to see it due to a protest.

Lazio's Brazilian defender Wallace gifted the ball to Kevin Strootman, who scored Roma's opener midway through the second half and Radja Nainggolan then doubled the lead for a 2-0 win Sunday.

Roma's celebrations were not as loud as usual because the club's most ardent supporters stayed away from the match in protest at plexiglass security barriers introduced at the start of last season in their area.

Normally filled with supporters waving huge banners, lighting flares and singing, half of the "curva sud" — southern end — of the Stadio Olimpico was left empty.

"It's ugly to see," said Strootman, who scored with a delicate chip shot over Lazio goalkeeper Federico Marchetti. "The fans who did come were very helpful to us and these were three very important points. Hopefully the others will come to the next matches because we need our fans."

The victory moved Roma back into second place, four points behind Juventus, which beat Atalanta 3-1 on Saturday.

AC Milan is level on points with Roma in third after coming from a goal down to beat visiting Crotone 2-1.

In the next round, Roma hosts Milan.

After Strootman's goal and an extended celebration, words appeared to be exchanged as Roma's players walked back onto the pitch alongside Lazio's bench.

Strootman appeared to toss water from a bottle at Lazio's Danilo Cataldi, who reacted by tugging the neck of Strootman's shirt as the Netherlands midfielder walked away.

That prompted both benches to get involved, leading to a general melee.

Cataldi, who had been on the bench, was red carded, while Strootman was shown a yellow.

Ten minutes later, Nainggolan scored with a long, bouncing shot inside the near post that appeared to surprise Marchetti.

Roma has now won four straight in the "Derby della Capitale" series, outscoring Lazio 10-2. Lazio's last derby win came in the 2013 Italian Cup final, while its last derby victory in Serie A came more than four years ago.

Neither side produced a clear chance in the first half of a match that was not pretty to watch.

"Since I've come to Roma I've never played in a beautiful derby," Strootman said. "Neither squad wants to make a mistake.

"We didn't have many chances but we won and got some important points," Strootman added.

Lazio is fifth, four points behind Roma.

Francesco Totti, Roma's 40-year-old captain, stayed on the bench.

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AC MILAN 2, CROTONE 1

Gianluca Lapadula is getting quite comfortable in his new role as AC Milan's centre forward.

Filling in for the injured Carlos Bacca, Lapadula earned a penalty and scored a late winner in a 2-1 win over visiting Crotone.

It was Lapadula's fourth goal in four matches — the first four of the Serie A career of a 26-year-old considered a late bloomer.

"Lapadula always plays with a lot of passion and that's his strength," Milan coach Vincenzo Montella said. "That was the type of goal that he scores. He's a real striker, the type that I like who can provide guarantees over the course of a season."

Diego Falcinelli had put Crotone ahead midway through the first half and Mario Pasalic equalized for Milan before the break.

With the score 1-1, M'Baye Niang had a penalty blocked by Crotone goalkeeper Alex Cordaz.

"It was a complicated match. Compliments to Crotone," Montella said. "It was a struggle to win but we really wanted it."

Milan has lost just one of its last 12 matches

Crotone is last with just six points from 15 matches.

Falcinelli's goal, his fifth of the season, was facilitated by poor defence from Milan that allowed him to score from the centre of the area uncontested.

Pasalic, who is on loan from Chelsea, scored his first goal in Serie A with a header following a corner.

Early in the second half, Lapadula was fouled inside the area to set up Niang's penalty but Cordaz dived in the right direction to make the save.

In the 86th, Lapadula took advantage of a rebound following a free kick to win it.

Lapadula, who scored 27 goals in 40 Serie B matches for Pescara before joining Milan, recently earned his first call up to Italy's national team. He could become an even more integral member of the Rossoneri if Bacca departs as rumoured in January.

Bacca was recently seen attending a match of his former club Sevilla, adding to speculation over his possible departure.

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OTHER GAMES:

Khouma Babacar scored an injury-time winner as Fiorentina beat struggling Palermo 2-1.

Federico Bernardeschi had put Fiorentina ahead with a header and Mato Jajalo equalized with a curling free kick for Palermo early in the second half.

In other matches, it was: Pescara 1, Cagliari 1; Sampdoria 2, Torino 0; and Sassuolo 3, Empoli 0.

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Andrew Dampf on Twitter: www.twitter.com/asdampf