Awaiting the winners of this tie in the grand finale is one of Palmeiras and Athletico Paranaense, who go head to head in the second semi-final.
Match preview
Flamengo picked up a sixth away win on the bounce across all competitions as they defeated Botafogo 1-0 at the Estadio Olimpico Nilton Santos on Sunday.
Dorival Junior's men opened the scoring just shy of the hour mark through Arturo Vidal and that was enough to secure all three points in Rio de Janeiro.
As a result, the Scarlet-Black have moved up to second place in the Brasileiro standings, seven points behind runaway leaders Palmeiras.
Coming up next is the challenge of an opposing side who have failed to come out on top in any of the two previous meetings between the teams.
Having won six of their last seven matches on the road, Thursday's visitors will be confident of securing a positive result here ahead of next week's return leg.
Velez Sarsfield were held to a second consecutive share of the spoils following a 1-1 stalemate against Independiente at the Estadio Libertadores de America on Sunday.
Alexander Medina's men went behind to Alan Sonora's opener in the 12th minute and looked set for defeat before Lucas Pratto restored parity in the final minute of normal time.
With just three points amassed from the last 15 available, El Fortin continue to languish in the lower echelons of the Liga Professional and sit bottom but one in the standings.
Twenty eight years on from their only Copa Libertadores triumph in 1994, Thursday's hosts will be keen to steal a first-leg advantage and bolster their chances of making it through to the final.
Velez Sarsfield Copa Libertadores form:
Velez Sarsfield form (all competitions):
Flamengo Copa Libertadores form:
Flamengo form (all competitions):
Team News
Pedro leads the Copa Libertadores scoring charts with eight goals in 10 matches so far and the Flamengo forward is one to keep an eye on here.
David Luiz missed his side's victory over Botafogo last time out but the Brazilian is expected back in the starting XI for Thursday's game.
Lucas Janson was at the double for Velez Sarsfield in the most recent encounter against Flamengo and the 28-year-old will be looking to deliver the goods once again.
Lucas Pratto will be pushing for a place in the starting XI here after finding the back of the net on his return to action from a suspension.
Velez Sarsfield possible starting lineup:
Burian; Jara, Matias, Gomez, Ortega; Garayalde, Caseres, Perrone; Orellano, Pratto, Janson
Flamengo possible starting lineup:
Santos; Filipe, Pereira, Luiz, Rodinei; Everton, Thiago, Gomes, De Arrascaeta; Pedro, Barbosa