RIO DE JANEIRO, May 13 (Xinhua) -- Diego Diellos scored twice as Bolivia's Nacional Potosi took a step toward the Copa Sudamericana knockout phase with a 3-0 home win over Uruguayan side Boston River on Tuesday.

Diellos broke the deadlock with a close-range strike, and he doubled the advantage by sweeping home a first-time effort after Victor Abrego's cross.

The visitors were reduced to 10 men in the 82nd minute when Alexander Gonzalez was shown a straight red card for violent conduct.

Carlos Preciado put the result beyond doubt by sending a free-kick into the bottom right corner in the third minute of stoppage time.

Nacional Potosi is now second in Group A with seven points from five games, a point behind leader Guarani. Boston River is last in the group with four points.

Elsewhere in the Copa Sudamericana on Tuesday, Gremio was held to a 1-1 home draw by Godoy Cruz, Lanus prevailed 1-0 at home to Vasco da Gama, Mushuc Runa won 1-0 at Union Santa Fe and Melgar clinched a 1-0 away win over Puerto Cabello. ■