Argentina's derby of derbies ends all-square
Leonardo Ponzio's early free-kick, which left keeper Agustin Orion groping at thin air, put River - promoted last season a year after their first ever relegation stunned fans across the nation - into an opening-minute lead.
And things looked even better for Matias Almeyda's men when Uruguayan Rodrigo Mora made it 2-0 midway through the second half at River's Monumental Stadium after former France star David Trezeguet linked-up with Carlos Sanchez.
But another Uruguayan, Santiago Silva, reduced the arrears with a 75th-minute penalty following German Pezzella's foul on Santiago Silva, before Walter Erviti rescued a point in the first minute of stoppage time.
The point left Boca in fifth place, three points ahead of their Buenos Aires rivals.
River had to reshuffle the pack with Almeyda having to take off defender Ramiro Funes Mori and Martin Aguirre after they suffered knee injuries in the opening period as 50,000 ferociously partisan fans looked on.
Leandro Gonzalez Pirez replaced Mori after just four minutes while Ariel Rojas came on for Aguirre just nine minutes later, disrupting River's solid start.
Although Boca will be the happier with the draw, in what was the first meeting of the pair in 17 months, a title challenge has not materialised so far this season as they trail leaders Newell's Old Boys by seven points after 12 games.
Elsewhere on Sunday, Belgrano Cordoba climbed to third spot courtesy of a 1-0 home triumph over bottom club Union Santa Fe.
Substitute Cesar Pereyra netted the game's only goal midway through the second half - shortly after the visitors had had defender Bruno Bianchi sent off.
Lanus were also 1-0 winners, Mario Regueiro's 58th-minute strike enough to sink Argentinos Juniors and lift the victors to fifth.