Universidad Catolica took the honours in Chile's top derby after beating Colo Colo 1-0 to join Union Espanola at the top of the Apertura.
Matias Rubio struck the winner at Estadio Monumental in Santiago after 14 minutes.
Milovan Mirosevic and Jeremias Caggiano wasted chances to extend Universidad's lead, while goalkeeper Cristopher Toselli denied Lucas Barrios on several occasions to preserve the slender advantage.
"We should have secured the victory in the first half," said Universidad defender Facundo Imboden.
"It should have been a comfortable 3-0 win, but we deserve the 1-0 win and the three points are very important."
Universidad joined Union on 16 points after they lost 2-1 at Cobreloa.