Spezia moved on to 31 points, which means that 19th-placed Cremonese, on 24 points, can no longer leapfrog them in search for safety.
Cremonese, who won one of their last six Serie A games and only four in total in the 2022-23 season, were hammered 5-1 at home by Bologna on Saturday.
"Today we showed that we deserve to be relegated," coach Davide Ballardini told a post-game press conference.
Cremonese had made a return to the Italian top flight after 26 years in 2021-22 when they finished second in Serie B, two points behind champions Lecce.