Dries Mertens is back in form and at the perfect time for Napoli as the Serie A title race heats up.

Mertens scored twice, including a stunning second-half strike, to help Napoli rally to beat Bologna 3-1 on Sunday and move back to the top of the league.

It took Mertens' tally to 13 Serie A goals but the Belgium international hadn't scored in the league since October before breaking his drought last week.

"Dries had a couple of low-key matches, which is very normal for any footballer," Napoli coach Maurizio Sarri said. "Then he got back to playing in a certain way, the goal is just a consequence of that."

Napoli moved a point above Juventus, which won 2-0 at Chievo Verona on Saturday. Lazio remained third but slipped 11 points behind Napoli after a 2-1 defeat at AC Milan. Roma hosts Sampdoria later.

There was more misery for Inter Milan as it was held to a 1-1 draw at relegation-threatened Spal.

After Juve's victory against nine-man Chievo, Napoli needed a win to move back into top spot.

However, it got off to the worst possible start as Rodrigo Palacio headed in Federico Di Francesco's cross after just 22 seconds.

But Bologna's lead lasted just four minutes. Following a short corner, Mario Rui crossed in from the left and Palacio deflected it off the crossbar before Ibrahima M'Baye accidentally turned the ball into his own net.

Napoli turned the match fully around shortly before halftime when Mertens converted a penalty kick after Adam Masina was adjudged to have pulled back Jose Callejon.

Mertens sealed the match in the 59th, racing down the left and cutting inside the area before curling a delightful effort into the far top corner.

Bologna coach Roberto Donadoni was furious at what he felt was a soft penalty, while his team was not awarded one of its own for Napoli defender Kalidou Koulibaly appearing to handle the ball. Both incidents were checked by video review.

"I feel like I'm living on another planet," Donadoni said. "These two incidents make you angry, then you think that this sort of penalty is only given to a team in the top eight places and below that no.

"The referee blows for a penalty in both situations, then he checks with the VAR and he can cancel it or give it, and instead he gives one and not the other and that's not right."

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ARM CONTROVERSY

Refereeing issues also surfaced in Milan's victory over Lazio as the Rossoneri's first goal appeared to come off Patrick Cutrone's arm rather than his head.

Neither the referee nor his assistants realized and the VAR was not consulted when Cutrone gave Milan the lead in the 15th minute.

Adam Marusic leveled five minutes later and Luis Alberto also hit the crossbar for Lazio before Giacomo Bonaventura headed in Davide Calabria's cross on the stroke of halftime.

Lazio has not won at Milan in Serie A since 1989. The two meet again at San Siro on Wednesday in the first leg of their Italian Cup semifinal.

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FREEFALL

Inter appeared to be a title contender less than a couple of months ago but has now fallen well off the pace.

Luciano Spalletti's side has now won just one of nine matches in all competitions — and that was a penalty shootout victory over third-division Pordenone.

Inter appeared on course for its first league win since the 5-0 thrashing of Chievo on Dec. 3 but Alberto Paloschi met Mirco Antenucci's cross-shot with a diving header to level in stoppage time.

Inter had taken the lead minutes after the break when Spal defender Francesco Vicari prodded Joao Cancelo's cross into his own net.

Spal had several chances to level as Inter sat back on its lead and was eventually punished.

Inter slipped to fourth, 13 points behind Napoli. Spal remained 18th in the 20-team league.

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OTHER GAMES

Hellas Verona gave itself hope of avoiding the drop with a surprise 4-1 victory at midtable Fiorentina.

On-loan Juventus teenager Moise Kean scored twice as Verona moved to within three points of 17th-placed Crotone, which drew 1-1 against fellow struggler Cagliari.

Cagliari was forced to play an entire half with 10 men and Crotone had a goal controversially disallowed in stoppages after several minutes of discussion with the video assistant referee.

Bottom side Benevento played even longer with a numerical disadvantage after goalkeeper Vid Belec karate-kicked M'Baye Niang in the 33rd minute and it went on to lose 3-0 at Torino.

Udinese was also reduced to 10 men but won 1-0 at Genoa.