Borja, Mastantuono on target in River Plate's 2-0 win over San Martin

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SAN JUAN, Argentina, Feb 22 (Reuters) - Miguel Borja and Franco Mastantuono broke through a sturdy San Martin defence in the second half to secure a 2-0 win for River Plate in the Argentine Primera Division Apertura tournament on Saturday.

River Plate, who are unbeaten in the campaign, moved to third in Group B with 15 points, a point above fourth-placed San Lorenzo who have a game in hand.

"Once we opened the scoring, we were able to find a little more fluid play, but we still need more from ourselves, more from the game," River Plate midfielder Enzo Perez told ESPN.

"Beyond the victory, which is very important... I think we must keep improving in our game and in who we are," Perez said.

San Martin did well to limit the visitors' passing game in the first half, and the hosts could have led when Alejandro Molina fired on target off a corner, but River Plate keeper Franco Armani kept it out.

Defender Molina almost struck again in the 42nd minute when his shot from outside the box caught Armani off position but defender Paulo Diaz blocked the attempt.

However, Molina was unable to stop Borja on the other end when a through ball from Pity Martinez found the Colombian forward in the San Martin box in the 56th minute.

Borja shook off Molina and an onrushing keeper Matias Borgogno with an athletic first touch to break the deadlock.

The visitors doubled their lead 13 minutes later when Mastantuono found the bottom of the left corner off Gonzalo Montiel's pass, condemning a winless San Martin to their third straight loss in the competition.

San Martin, 14th in Group B, remained on three points after seven matches, four points below the top eight who qualify for the round of 16.

River Plate host Estudiantes next Saturday. (Reporting by Chiranjit Ojha in Bengaluru; Editing by Michael Perry and William Mallard)