Reigning champions Inter came through what was supposed to be a tough test at the Stadio Olimpico with flying colours and are three points off the Scudetto pace with a game in hand.
Substitute Zaniolo decided a hard-fought encounter in Sardinia by stroking home Raoul Bellanova's cut-back in the 66th minute and moving Atalanta five points clear.
Edoardo Bove has had a defibrillator fitted after the Fiorentina midfielder's on-pitch cardiac arrest earlier this month, according to widespread Italian media reports on Tuesday.
Fiorentina earlier remained on Napoli's heels after their 1-0 home win over Cagliari in their first league match since midfielder Edoardo Bove's sudden collapse last weekend.
Edoardo Bove is conscious and alert in hospital after his sudden collapse which caused Fiorentina's match with Inter Milan to be called off, the Serie A club said on Monday.
Fiorentina's Serie A match with Inter Milan was stopped on Sunday after midfielder Edoardo Bove suddenly collapsed to the ground.
"It's too early to talk about the title. All we can do is look out for how we develop as a team, work to improve and win every match we play. But now is not the moment to talk about the title," said Lukaku.
Juventus remain the only unbeaten side in Serie A but their seventh draw of the season means they remain sixth in the standings and are now three points behind leaders Inter Milan. Milan stay seventh, six points behind Juve, though they have played one game fewer.
Simone Inzaghi's side are provisionally ahead of Napoli after netting all five of their goals in the opening 45 minutes at the Stadio Bentegodi through a Marcus Thuram brace and further strikes from Joaquin Correa, Stefan de Vrij and Yann Bisseck.
Italy midfielder Frattesi rammed home the decisive strike in the third minute of stoppage time of an incredible match at the San Siro full of late drama.
Adrien Rabiot's second-half goal earned Juventus a 1-0 home win over AS Roma on Saturday that took them within two points of Serie A leaders Inter Milan.
Defending Serie A champions Napoli saw their non-winning league ways continue Friday with a goalless draw against mid-table Monza.
Yann Bissek's first goal in Italy just before half-time at the San Siro and a late finish from Nicolo Barella were enough for Inter to bounce back from cup defeat to Bologna midweek and keep closest challengers Juventus at bay.
Inter's dynamic attacking duo made sure their team took full advantage of closest rivals Juventus only drawing at Genoa on Friday to put daylight between Simone Inzaghi's side and the rest of the chasing pack
Paulo Dybala picked out Lukaku with a clever cross as the Belgium striker headed Roma in front in the fifth minute at the Stadio Olimpico.
Turkey playmaker Hakan Calhanoglu set up a goal and scored another as Inter Milan moved back to the summit of Serie A with Saturday's comfortable 4-0 home win over Udinese.
The centre-back rose highest shortly after the break to nod in the only goal of a closely contested match between two of Italy's footballing powerhouses.
Lautaro Martinez ensured that Inter Milan kept hold of their two-point lead at the top of Serie A as he struck in Sunday's scrappy 1-1 draw at closest rivals Juventus.
AC Milan starlet Francesco Camarda made history on Saturday after becoming the youngest ever player to play in Serie A during Saturday's 1-0 win over Fiorentina.
