Arkadiusz Milik came off the bench to snatch a late 2-1 win for Napoli over Atalanta on Monday that consolidated second place in Serie A and reduced the gap on leaders Juventus to eight points.
Polish forward Milik scored the winner five minutes from time shortly after coming on after Fabian Ruiz had put the visitors ahead just two minutes into the clash in Bergamo and former Napoli man Duvan Zapata had pulled Atalanta level 11 minutes after the break.
Napoli close the gap on Juventus, who pulled 11 points clear with a 3-0 win at Fiorentina on Saturday with Cristiano Ronaldo scoring from the spot to bag his 10th goal in 14 games.
"It's a very, very important goal for all of us," said Napoli coach Ancelotti.
"Milik went through a difficult period because he didn't play consistently, but he remained motivated and focused, so deserves this."
Ancelotti's side came out firing on all cylinders after their title hopes took a serious hit with a goalless draw against bottom club Chievo last weekend.
The coach stuck with the same starting line-up that beat Red Star Belgrade 3-1 in the Champions League midweek.
Captain Marek Hamsik started the move that led to the opener with just a minute on the clock, passing to Lorenzo Insigne who crossed for Spaniard Ruiz to tap in his third goal since joining Napoli from Real Betis.
Insigne was ruled offside early as his volley rattled the bar with a lob shortly after the Italian international forward shot wide as he slipped.
Zapata tested Napoli goalkeeper David Ospina in the first half with defender Raul Albiol also clearing off the Colombian after the break.
But the former Napoli forward broke though on 56 minutes when Hans Hateboer headed the ball down and he blasted in from close range.
Milik came on for Dries Mertens after 81 minutes and four minutes later picked up a Mario Rui cross to fire in the winner for his fifth goal this season.
And the Polish striker said the win gaves his side confidence ahead of next week's decisive Champions League clash against Liverpool at Anfield.
"Before the Champions League, we have another tough Serie A game against Frosinone. Of course we want to beat Liverpool, we know it won't be easy, but we believe in ourselves," said Milik.
Napoli move three points ahead of Inter Milan, who played out an entertaining 2-2 draw against Roma in the Stadio Olimpico on Sunday.
Atalanta are in 11th position after their second consecutive defeat.
Luciano Spalletti's Inter travel to Turin next Friday to face Juventus in the hope of derailing their bitter rivals' title procession, with Napoli hosting second from bottom Frosinone on Saturday.