The 1985 Libertadores Cup winners were helped by San Martin's 3-1 defeat at River Plate that sent them back down to the second-tier Primera B Nacional after two seasons in the top flight.
San Martin join Union and Independiente as the teams relegated after finishing in the bottom three of the relegation standings, a separate table of teams' average points over three seasons.
Substitute Pablo Hernandez headed the only goal from a corner in the 86th minute as Argentinos coach Ricardo Caruso Lombardi celebrated yet another success as a specialist in steering teams clear of the drop.
Caruso, often called in as a "fireman" by relegation-threatened clubs, has previously steered Tigre, Quilmes, Racing Club, Newell's and most recently San Lorenzo last year clear of danger.
"I've got nothing but thanks for this group of players, also the fans. We got together at the right moment and we're safe," Caruso told reporters.
"I feel really emotional because the players made a huge effort...They became men all of a sudden.
"It's an unhealthy job, you can't believe how I suffered," added Caruso, known for his verbosity in front of the cameras and microphones.
Independiente's first relegation was the biggest shock since fellow Buenos Aires giants River Plate suffered the same fate two years ago.
Argentinos' victory did not dampen Newell's fans' celebrations at their Marcelo Bielsa stadium in Rosario after their team had secured the title in midweek with a match to spare.
There were two championships in the Argentine 2012/13 season, 'Inicial' and 'Final', with winners Velez Sarsfield and Newell's meeting in a grand final in Mendoza next Saturday.
