River substitute German Pezzella cancelled out Lisandro Magallan's first-half opener as the two heavyweights shared the spoils in a match that saw both teams reduced to 10 men in sodden conditions.
Argentina international Fernando Gago saw red for Boca four minutes before half-time, while River defender Ramiro Funes Mori was dismissed with six minutes remaining at the Estadio Monumental Antonio Vespucio Liberti.
The result ensured River's place atop the summit with 22 points from 10 matches, despite three consecutive draws.
Boca are eight points further back in ninth position.
The last league meeting between the two teams in March saw River win 2-1 at La Bombonera, ending their 10-year drought without victory at Boca's stadium.
Boca were understandably desperate to exact revenge and they made an ideal start in terrible conditions, Magallan opening the scoring in the 22nd minute.
Federico Carrizo floated in a free-kick and Magallan was on hand to bury the half-volley.
Hosts River came close to equalising but they were denied by the crossbar shortly after.
Boca received a double blow four minutes before the break after Gago was sent off for a handball in the area.
River failed to capitalise, however, as Uruguayan striker Rodrigo Mora skied his spot-kick over the crossbar.
Boca were pressed back in the second half as River made the most of their numerical advantage, and the visitors were eventually opened up in the 78th minute.
Within two minutes of replacing Carlos Sanchez, Pezzella pounced on his own rebound after goalkeeper Agustin Orion failed to deal with his initial header.
River played the final six minutes with 10 men after Funes Mori was punished for a lunging tackle.
In other results, fourth-placed Estudiantes recorded back-to-back wins thanks to a 2-1 victory at lowly Olimpo.
Velez Sarsfield's dismal run continued, losing 2-0 at Gimnasia La Plata as their winless streak extended to six matches.
Newell's Old Boys were held to a 1-1 draw at basement side Quilmes.
South American champions San Lorenzo were beaten 2-0 by Tigre and Defensa y Justicia accounted for Arsenal 2-1.
Meanwhile, Belgrano came from behind twice to draw 2-2 with Banfield.
