Lazio's determined bid to gatecrash the Champions League places was thwarted as Fiorentina recovered to beat them 3-2 at Stadio Artemio Franchi on Saturday evening.
Simone Inzaghi's men have played catch-up with top-three clubs Juventus, Roma and Napoli all season long but a three-game winning streak had brought them within seven points of the Azzurri.
However, Saturday's result confirmed Roma and Napoli's place in the Champions League for next season as Lazio can now finish no higher than fourth.
After a goalless first half, Balde Keita Diao's 55th-minute opener -- his 15th Serie A goal in 2016-17 -- temporarily narrowed Napoli's advantage to four points.
The Senegalese striker turned Luis Alberto's pass beyond Ciprian Tatarusanu before wheeling away in celebration. However, Khouma Babacar levelled proceedings with a header on 67 minutes.
Fiorentina, who still harbour hopes of qualifying for the Europa League, turned the game on its head when substitute Nikola Kalinic converted Cristian Tello's saved shot in the 73rd minute.
Cristiano Lombardi then inadvertently doubled the Tuscans' lead -- also confirming their eventual victory -- with an own goal as he tried to clear a rebounding Kalinic effort.
Lazio were certainly not ready to roll over and give up and 20-year-old midfielder Alessandro Murgia ensured a nervy finale with his headed finish from a Luis Alberto cross nine minutes from time.
In the late game, Gerard Deulofeu spared AC Milan's blushes with a last-gasp goal, but at full-time it was their opponents Atalanta who were jubilantly celebrating the point from a 1-1 draw.
The result guarantees the Bergamo club's return to European competition after a 26-year absence as they cannot now be dislodged from fifth place over the last two games of the season.
Gian Piero Gasperini's men will play in the Europa League next year and still have ambitions of breaking into the top four. They were set on their way to closing to within two points of Lazio by Andrea Conti.
The Nerazzurro right-back was best placed to exploit Gianluigi Donnarumma's poor attempt to collect Leonardo Spinazzola's cross one minute before half-time, and Atalanta were deservedly ahead.
Milan's teenage goalkeeper Donnarumma spent the second half under siege and his colleagues eventually repaid him for his efforts when Deulofeu beat Atalanta stopper Etrit Berisha in the 88th minute. The on-loan Everton winger made it a fourth straight away draw for the ailing Rossoneri.