Mariano Soso's side are rooted to the bottom of the section with a solitary point to their name, while their visitors occupy third place with three points and can officially end their hosts' continental journey here.
Match preview
One year on from enjoying their best-ever run in South American football - getting to the semi-finals of the Copa Sudamericana before being seen off 6-0 by Independiente del Valle - the step-up to Libertadores level has been a miserable affair for Melgar.
The Domino have never before reached the knockout stages of the continent's premier competition, and taking a quick glance at their showings in the 2023 section, it is easy to see why, as Soso's men have suffered three successive defeats in Group H since holding Olimpia to a draw on the opening matchday.
The most recent of those beatings came at the hands of 10-men Atletico Nacional, who did not have it all their own way at the Estadio Monumental de la UNSA on May 24 but eventually got over the line thanks to Danovis Banguero's 88th-minute header, leading Melgar on the brink of elimination.
Defeat for the hosts this week would consign them to a fourth-placed finish with one game to go, but a point or three would keep them in contention for a return to the Copa Sudamericana; both Nacional and Olimpia boast unassailable leads in the last-16 positions.
Soso's men have been the draw specialists in the Peruvian Liga 1 this season and stayed true to their name at the weekend also - throwing away a two-goal lead in a 2-2 stalemate with Universidad Cesar Vallejo - leaving them 10th in the rankings and some way off the continental conversation at this point of the campaign.
Similarly, a spate of unsightly results both domestically and continentally means that summertime joy is sparse for Patronato, but the Red and Black are still in with a slim chance of forcing their way into the top two of Group H if results go their way over the next few weeks.
Walter Otta's side were no match for Olimpia in their most recent Copa Libertadores outing, as strikes in either half from Ivan Torres and Diego Torres sealed a straightforward 2-0 win for the Paraguayan powerhouses, and Patronato's top-two dreams will be dashed if they fail to win on Tuesday.
Otta's men qualified for the Copa Libertadores in peculiar circumstances too, as they won the 2021-22 Copa Argentina while simultaneously suffering relegation from the Argentine Primera Division, and their bid to return to the top tier is yet to get going.
Indeed, Patronato are languishing in 11th place in the Primera Nacional following a 2-1 loss to league leaders Agropecuario Argentino at the weekend - their third consecutive loss away from home - and the visitors have failed to score more than one goal in a road match since August.
However, Patronato taught Melgar a footballing lesson in a 4-1 romping when the sides locked horns in Argentina last month, and replicating such an impressive success would see the Red and Black bring their hosts' continental journey to a premature end yet again.
Melgar Copa Libertadores form:
D
L
L
L
Melgar form (all competitions):
Patronato Copa Libertadores form:
L
L
W
L
Patronato form (all competitions):
Team News
Melgar lost attacking midfielder Tomas Martinez to injury during their matchday four defeat to Atletico Nacional, and having sat out the recent draw with Cesar Vallejo, it is unclear if the 28-year-old will be given the green light for Tuesday.
Left-back Paolo Reyna and winger Luis Iberico are both set to miss out due to knee concerns, but Soso has an established 3-5-2 setup and should not stray away from that tried-and-tested formula with so much at stake.
However, Jhamir D'Arrigo may give his manager food for thought up front after coming off the bench to score his side's second at the weekend, with Pablo Magnin potentially fearing for his place.
As for Patronato, Otta has no fresh fitness problems to report from the weekend's second-tier defeat, but the 49-year-old made no fewer than three half-time changes at the weekend and should not be averse to rotation for Tuesday's pivotal contest.
Nazareno Solis was one member of the sacrificed half-time trio - despite scoring his side's goal on the day - but the Boca Juniors loanee ought to hold his spot out wide as Mateo Levato gets the nod in the final third.
Melgar possible starting lineup:
Caceda; Archimbaud, Galeano, Deneumostier; Bordacahar, Orzan, Cabrera, Tandazo, Cavero; Cuesta, D'Arrigo
Patronato possible starting lineup:
Salva; Ruiz Diaz, Ojeda, Gonzalez, Cobos; Domingo, Chamorro; Solis, Barinaga, Esquivel; Levato
We say: Melgar 1-1 Patronato
Given Patronato's repeated failings in front of goal away from home, there should be no repeat of the 4-1 thumping they dished out on Melgar last month, especially with the hosts fighting for their lives at the bottom of the section.