Salernitano looked in serious danger of decline when David Nicola took office in February, sitting at the bottom of the table with three wins in 23 games.
However, Nicola inspired a revival when his team scored 15 points in a series of seven league games to advance to the final round by two points from Cagliari.
However, Udinese were big when Gerard Deulafeu, Elijah Nestorowski and Jenoma Destini Udogi beat Nicolas 3-0 before Monday’s transition (AEST).
Udinese captain Roberto Pereira added fourth after the break when the Friulians achieved the best set of points in Serie A (47) since the 2012-13 season (66).
This meant that “Cagliari” would have stayed with the victory in “Venice”, but Alessandro Agastini was able to play only a draw, as “Rosabela” for the sixth time in its history was eliminated in Serie B.
The failure of “Cagliari” brought Salernitan the first-ever survival in Serie A, failing to do so in two other attempts in 1947-1948 and 1998-1999.
Salernitana also became the first team to remain in place, despite conceding at least 78 goals in one top campaign after Livorno (79 in 1929-30) and Lucchese (82 in 1947-48, 79 in 1949- 50).
Meanwhile, Cagliari joins Venice and Genoa in Serie B, and the trio will seek to recover next season.