With demotion rivals Hellas Verona getting the better of Lecce at the weekend, Dejan Stankovic's men needed a win on Monday evening to delay their seemingly inevitable drop to Serie B.
However, a third straight loss in the top flight sealed Sampdoria's fate, as first-half strikes from Roberto Pereyra and Adam Masina propelled Udinese to a straightforward win.
Pereyra took just nine minutes to break the deadlock for Udinese, before another former Watford man in Masina headed home from Sandi Lovric's cross to double the hosts' advantage in the 34th minute.
Sampdoria could not mount a storming fightback in the dying embers and now sit on just 17 points from their 34 games, 13 points worse off than 17th-placed Verona with just 12 points left to play for.
The Blucerchiati last suffered relegation to Serie B in the 2010-11 campaign, but they were promoted straight back to the top flight at the first time of asking via the playoffs.
During Sampdoria's subsequent 11-year stay in the top flight, they finished as high as seventh in the 2014-15 season, but they just about kept their heads above water last term with a 15th-placed finish.
Financial problems have also bedevilled the 1991 Italian champions all season long, and there are concerns that the Blucerchiati could be declared bankrupt ahead of the new season.