Pursuing back-to-back continental crowns, Flu qualified for the knockout stage with a round to spare and can now complete a year without being beaten in South America's top club competition; Alianza, meanwhile, must win to have any hope of going through.
Match preview
By beating Cerro Porteno 2-1 at home earlier this month, Fluminense reached 11 points and can no longer be caught by any of their competitors in Group A, and they will take part in the Copa Libertadores elimination phase for a third time in four years.
Flu's last defeat in CONMEBOL's top tournament came in June of last year, to River Plate, and as this season's last-16 stage is scheduled to take place in August, the 2023 champions can go 12 months without losing a Libertadores contest - a run of 13 games undefeated.
Despite his unsuccessful dalliance with Brazil's national team, head coach Fernando Diniz is close to becoming the Rio club's longest-serving coach this century, with only one month to go before reaching that mark, and his side have picked up 10 more points since drawing with Alianza in Peru.
After a midweek win over Sampaio Correa in the Copa do Brasil, Fluminense are unbeaten in their last six matches at the Maracana, scoring multiple goals on each occasion - including that defeat of Cerro Porteno, which featured strikes from veteran pair Paulo Ganso and Marcelo.
A slow start to this year's Brasileiro has proved a concern for Diniz, though, as Flu sit inside the bottom four after taking just five points from their first six league fixtures; so building more momentum before a weekend clash with fellow strugglers Juventude will be the Tricolor's target on Wednesday.
Since Kevin Serna's goal earned Alianza a creditable 1-1 draw in last month's reverse fixture, the Lima club have picked up only four more points and are locked in a three-way battle with Cerro Porteno and Colo-Colo to progress from Group A.
Like Fluminense, Los Blanquiazules have recently endured a difficult time domestically, with six defeats and 11 wins leaving them a distant fourth in Peru's Liga 1 table.
Soon after scrapping out a 3-2 victory over Deportivo Garcilaso, Alianza lost 3-0 away to Cusco last time out, and they must now take a significant step up in class, fighting it out for three points with one of Brazil's football giants at the Maracana.
It is clear from local reports that Alejandro Restrepo's job could on the line, and the Colombian coach - who previously won his home nation's league title with Deportivo Pereira - will have to keep his team in continental competition in order to survive.
That means either qualifying for the Copa Libertadores last-16 or finishing third in Group A to drop into the second-tier Copa Sudamericana: to achieve the former, Alianza must win and hope Cerro Porteno and Colo Colo draw; the latter would require at least a draw in Rio de Janeiro, plus either side winning the other match.
Fluminense Copa Libertadores form:
D
W
D
W
W
Fluminense form (all competitions):
L
D
W
L
W
W
Alianza Lima Copa Libertadores form:
D
L
D
D
D
Alianza Lima form (all competitions):
L
D
L
D
D
D
Team News
Soon to be joined by Thiago Silva - who will make his Fluminense return early next month - another vastly experienced defender, Felipe Melo, reached 100 games for the Rio club earlier this week, and the 40-year-old should start on Wednesday evening.
While Lima could return to the squad after being ruled out of Flu's cup win by illness, Manoel (muscular), Andre (knee), Samuel Xavier (foot) and Douglas Costa (thigh) are all sidelined by injury, alongside long-term absentee Lele (ACL).
Supporting last term's top scorer German Cano up front, Colombian winger Jhon Arias has recorded the hosts' most goal contributions in 2024 (nine), level with Lele on six goals and veteran playmaker Paulo Ganso on three assists.
Meanwhile, Alianza boss Alejandro Restrepo may be able to call upon striker Pablo Sabbag for the first time this year, after the Colombia-born striker was injured on international duty for Syria.
Sabbag will provide competition for Hernan Barcos, Kevin Serna and Cecilio Waterman up front, with his comeback leaving only Gabriel Costa and Jiovany Ramos in the treatment room.
Fluminense possible starting lineup:
Fabio; Guga, Melo, Martinelli, Marcelo; Alexsander, Lima; Arias, Ganso, Keno; Cano
Alianza Lima possible starting lineup:
Campos; Ramos, Zambrano, Garces; Zanellato, Cabellos, Arregui, Freytes, Rodriguez; Barcos, Serna