Argentina's Velez went down 1-0 away to Emelec thanks to an own goal by striker Facuando Ferreyra and had defender Fernando Tobio sent off after 62 minutes in their Group Four match on Tuesday.
The opening 15 minutes of the second half at the George Capwell stadium in Guayaquil was the decisive spell with Ferreyra deflecting Marcos Caicedo's 49th-minute shot past wrong-footed keeper Sebastian Sosa and Tobio being booked for the second time.
Uruguay's Nacional, dominated almost throughout their Group One match at Parque Central in Montevideo by Barcelona, the twice finalists from Guayaquil, were fortunate to salvage a 2-2 draw in a dramatic finale after going two goals down in 25 minutes.
Man of the match Damian Diaz put Barcelona ahead with a brilliant strike from outside the penalty area in the 17th and his fellow Argentine Ariel Nahuelpan increased the lead.
However, two veteran substitutes dragged Nacional back into the game with Sebastian "Loco" Abreu heading their first goal in the 70th minute as former Inter Milan winger Alvaro Recoba launched a series of counter-attacks.
Both sides were reduced to 10 men when Barcelona's Jose Perlaza was sent off in the 75th minute and defender Alejandro Lembo of Nacional followed.
Although Lembo was booked for the second time in the 77th, he did not leave the field for another five minutes until Chilean referee Enrique Osses realised he had shown the player the yellow card earlier in the match.
Osses then denied Barcelona what looked a blatant penalty on Diaz in the dying minutes, play went back to the other end and Recoba laid on striker Ivan Alonso's headed equaliser.
Universidad de Chile beat Deportivo Lara of Venezuela 2-0 at home with two goals from Sebastian Ubilla in their opening Group 7 match in Santiago.