The victory prevented Juan Sebastian Veron's Estudiantes from taking the lead in the Apertura championship, which is led by San Lorenzo after their 1-0 win over Rosario Central on Friday.
San Lorenzo have 19 points from nine matches, one more point than Colon, Argentinos Juniors and title holders Velez Sarsfield. Estudiantes, Independiente, Banfield and Newell's all have 17 points.
Former Boca Juniors defender Schiavi took a 78th minute penalty after a handball by Estudiantes midfielder Rodrigo Brana. Keeper Damian Albil parried Schiavi's spot kick but the 36-year-old netted the rebound.
Uruguayan striker Joaquin Boghossian headed Newell's in front in the 29th minute from Jorge Achucarro's cross only for Leandro Benitez to equalise within a minute after a solo run through the defence.
The victory will have boosted their confidence for next Sunday's "superclasico" away to arch-rivals River Plate, one of the world's great derbies.
"That was our best performance (of the championship)...We feel we have an obligation to fight for the championship," Boca playmaker Juan Roman Riquelme told reporters.
Goalkeeper Daniel Vega, back in the side after Nicolas Navarro was dropped following last weekend's 3-1 home defeat by Independiente, pulled off a string of fine saves to keep River in the match.
"To shut up our goal was one thing we were betting on," coach Leonardo Astrada said.
