None of the teams in the top five of the Clausura standings before the weekend earned wins as second-placed Velez Sarsfield drew 1-1 with Colon in Santa Fe, midfielder Victor Zapata equalising in the fourth minute of added time.
River are top with 19 points and Velez, who play San Lorenzo on Wednesday in a game suspended last month because of crowd violence, have 18.
Three teams are tied for third with 17 points including title holders Estudiantes, held 2-2 by Olimpo, and Godoy Cruz, who ended Argentinos Juniors' unbeaten run with a 1-0 win on Saturday.
Tigre striker Denis Stracqualursi hit a hat-trick at Boca's Bombonera that put him top of the scorers' list with a tally of eight but he left disappointed by the draw.
"Although it was nice to get the three goals, I'm left with a sour taste, this was a winnable match and we didn't win," Stracqualursi told Futbol Para Todos.
The striker stunned the Boca fans by putting Tigre 2-0 up inside 35 minutes as he stole ahead of his marker twice to head past keeper Cristian Lucchetti.
But Boca, who have struggled for form all year, fought back and two goals in the last three minutes of the first half including Juan Roman Riquelme's equaliser put them level at half-time.
A Stracqualursi penalty after young defender Enzo Ruiz pulled midfielder Roman Martinez down put Tigre ahead again with 20 minutes to go.
But a fine shot from outside the box into the top corner 12 minutes from time by Argentina full back Clemente Rodriguez salvaged a point, only their fifth in five home matches, for Boca.
Thank you for reading 5 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1