Meanwhile, with three matches already played, River were still waiting for Colombia striker Teofilo Gutierrez's papers in a transfer from Cruz Azul of Mexico to come through so he can finally make his debut at home to Colon on Sunday.
The 35-year-old Trezeguet traded several passes with Argentina winger Maxi Rodriguez before volleying the ball into the top corner to seal the victory in the final minute of Friday night's match.
Paraguay right back Marcos Caceres had given Newell's the lead early in the second half of the match in the "Inicial" championship, first of two in the season.
"This is a team who don't lose their values, they like to control the ball, enjoy themselves, for the forwards it's a pleasure to play with these players," Trezeguet said of the side built by former coach Gerardo Martino before he departed for Barcelona last month.
Newell's, now under coach Jorge Berti, are third in the standings with seven points from three matches. They are two points behind promoted leaders Gimnsia, who won 2-1 at Belgrano and visit Newell's in Rosario on Tuesday.
Racing Club, who enjoyed a strong finish to last season, are bottom of the 19-team league on one point after crashing to their third defeat in four matches, 2-0 at home to Arsenal, who are second on eight points.
"We're on the edge of the abyss but we'll pull through," Racing coach Luis Zubeldia told reporters.