Boca needed only 50 seconds to take the lead as Juan Roman Riquelme set up midfielder Pablo Ledesma to score the opening goal.

Boca completely dominated the opening half but River goalkeeper Juan Pablo Carrizo was in sensational form, keeping the deficit to one goal.

However, River were a different team in the second half and Daniel Passarella's side were back on level terms in the 49th minute when Mauro Rosales equalised with his first goal since his transfer to the Buenos Aires side from Ajax.

Both teams had chances to grab a winner but Martin Palermo, Pablo Ledesma, Fernando Belluschi and Marco Ruben all missed opportunities.

"It was very difficult to play at the same level in the second half as we had in the first half. But after 25 minutes of the second half, we improved again," Boca coach Miguel Russo said.

"I am very satisfied with the performance level of the team but to lose two points, especially when you merit a win is not nice."

The result leaves San Lorenzo alone at the top with 25 points. Boca are second, two points behind, while River have 17 points with a postponed game against Colon in hand.

In La Plata, Apertura champions Estudiantes were held to a goalless draw by Lanus to remain third, six points behind the leaders.

Newell's Old Boys continued their resurgence under coach Pablo Marini, claiming their fourth win in six games with a 2-0 away win against Belgrano.

Rosario Central moved off the bottom of the table with a 3-0 win over Nueva Chicago, thanks to a penalty by Cristian 'Kily' Gonzalez and goals by Damian Diaz and Gonzalo Belloso.

Velez Sarsfield took a 3-0 lead against Banfield but had to hold on in the second half as the home side battled back to cut the deficit to 3-2.

Gimnasia y Esgrima Jujuy and Argentinos Juniors played out a goalless draw in the day's remaining game.