Sandro Tonali scored in stoppage time as AC Milan came from behind to win 2-1 at Lazio on Sunday and retake top spot from Inter Milan in Serie A, while Napoli's title hopes appear over after their meltdown in Empoli.
Ciro Immobile gave Lazio an early lead at the Stadio Olimpico in Rome, but Olivier Giroud levelled shortly after half-time before Tonali's late heroics kept Milan firmly in the title hunt.
They moved back two points above of Inter, who beat Roma 3-1 on Saturday and have a game in hand Wednesday away to Bologna. Inter also knocked Milan out of the Italian Cup semi-finals in midweek.
Ciro Immobile became the leading active scorer in Italy's top flight when he turned in a cross from Sergej Milinkovic-Savic inside four minutes.
The Italy international's 181st Serie A goal took him past veteran Sampdoria striker Fabio Quagliarella as Immobile extended his league-leading haul for the season to 26.
But Giroud poked in from after excellent work from Rafael Leao, and Milan won it at the death as Zlatan Ibrahimovic nodded across for Tonali to force home following a poor defensive header by Francesco Acerbi.
"My players are lions," said Milan coach Stefano Pioli.
"I am so proud of my players and if I was in their shoes, I'd be angry, as people don't give them enough credit," he told DAZN.
Napoli's Scudetto prospects are hanging by a thread after they blew a two-goal lead late on and crashed to a shock 3-2 loss at Empoli.
Luciano Spalletti's side were 2-0 ahead with 10 minutes to go before Scottish midfielder Liam Henderson sparked a revival for the hosts who scored three goals in an eight-minute spell.
With four matches to play this season, Napoli are seven points behind Milan and five adrift of second-placed Inter.
Napoli have not won the Serie A title since the days of club legend Diego Maradona who led them to their two league crowns in 1987 and 1990.
Dries Mertens opened the scoring just before the break with Lorenzo Insigne adding a second eight minutes after the interval.
But Napoli's defence collapsed in the absence of the suspended Kalidou Koulibaly