San Lorenzo, the favorite club of Argentina-born Pope Francis, wraps up the first half of the season next weekend at Velez Sarsfield and Lanus plays at Newell's.
Boca needed a victory to stay in the chase, but didn't get it.
Juan Sanchez Mino scored for Boca to level at 2-2 in the 65th. Marcos Astina gave Lanus a 1-0 lead in the 22nd, Nicolas Blandi equalized in the 50th and Oscar Benitez put Lanus back on top in the 61st.
In other results on Saturday: Colon 0, Velez Sarsfield 2; Tigre 3, Atletico Rafaela 1; Arsenal 1, Belgrano 4; All Boys 3, Newell's 1.
On Friday: Godoy Cruz 0, Olimpo 1; Rosario Central 1, Racing Club 1.