La Dea had a surprisingly poor home record in Serie A this season, with just one victory, three draws and two defeats.
Robin Gosens, Hans Hateboer and Matteo Lovato were out of action, but Rafael Toloi returned. Nikolaou sat out a ban for Spezia, with Leo Sena, Kevin Agudelo and Medhi Bourabia injured.
Josip Ilicic’s angled drive flashed across the face of goal, but Spezia took a shock lead out of nowhere. Juan Musso got one hand to a sudden long-range Daniele Verde strike and palmed it onto the crossbar, but M’Bala Nzola was quickest to react on the rebound.
Mario Pasalic fired in the equaliser from six yards after Davide Zappacosta nutmegged one defender while squeezing past another down the right, pulling back from the by-line as Duvan Zapata missed the ball, but the Croatian did not.
Duvan Zapata’s effort was charged down at the near post after a spectacular build-up move with nutmeg and back-heel flick.
Joakim Maehle was sent clear on the counter and saw his shot charged down from six yards by Jacopo Sala, but he put his arm up at the last second and it had to be a penalty. Duvan Zapata saw his weak and central spot-kick parried by Ivan Provedel and put out for a corner by defenders, but it had to be retaken because of encroachment and the goalkeeper not having his feet on the line. The Colombian stepped up again and this time blasted into the roof of the net.
Spezia tried to fight back, but Duvan Zapata sprinted away on the counter from midfield and rolled across for Pasalic to sweep home undisturbed.
Hristov made a decisive interception to prevent Duvan Zapata creating another goal for Pasalic at the hour mark, while Musso used his legs to parry Nzola’s finish on the counter-attack.
Ruslan Malinovskyi’s trademark rocket skimmed the woodwork and Duvan Zapata stung Provedel’s gloves, but Luis Muriel broke his goal drought off the bench.
Pasalic was involved again, this time with a cross from the left, as Muriel hit it on the volley with his left foot from 12 yards into the near bottom corner.
Musso denied Ebrima Colley’s strike, but Malinovskyi completed the rout in the final minute from the edge of the penalty area.
Spezia did get some consolation with Nzola’s second of the game, knocking down and firing in a corner at the back post.