Sergio Romero was a reserve goalkeeper at Manchester United. Before that, he was a reserve at Sampdoria, and also a reserve in a loan spell at AS Monaco. He was even a reserve last year when he went back home to Argentina and joined Boca Juniors.

But while he was spending all of that time on benches across Europe, he was also becoming the most capped goalkeeper in Argentina’s history. Now 36, Romero would seem to have no chance of winning the shirt back from Emiliano Martínez. But, in the twilight of his career, he still has important things to do — like interrupting Brazil’s dominance of the Copa Libertadores, South America’s Champions League.

Evenly split between Flamengo and Palmeiras, Brazilian clubs have claimed the last four titles. The last three times they also provided the beaten opposition in the final, a pattern that is being reproduced this year. When the semifinals kick off this week, three of the four teams are from Brazil. The clash between Fluminense and Internacional brings the guarantee of one Brazilian side in the final to be staged in Rio de Janeiro’s Maracana stadium on Nov. 4. Champions in 2020 and 2021, beaten semifinalists last year, Palmeiras are also widely expected to make it through to the finale, while their opponents Boca Juniors provide the last hope for the rest of the continent. Which means that there is a lot riding on Romero.

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There is a chink of light for Boca as this might be a good time to face Palmeiras. The Brazilian side are well drilled under their excellent and highly promising Portuguese coach Abel Ferreira, but the loss through injury of wily winger Dudu has hit them hard. The goals have dried up. In the last four matches they have found the net once, deep in stoppage time against relegation-threatened Goias. Boca will hope, then, that they can keep the game tight.

For all of their Libertadores pedigree (six titles, the last in 2007), this year they were not seen as the most obvious challengers to the Brazilian stranglehold. Their form has not been impressive all season, leading to the replacement of coach Hugo Ibarra by the more experienced Jorge Almiron. But Boca have benefited from the luck of the draw. Their group was one of the weakest in the competition, but their progress through it was laboured. Then, in the knockout stages, are yet to win a single game, fighting out four consecutive draws (0-0 and 2-2 against Nacional of Uruguay, followed by two goalless matches against neighbours Racing). Both ties went to shootouts, and this is where Romero comes in.

As opponents ran in to take their penalties, the big keeper looked even bigger. Romero appeared to fill the goal. Against Nacional he threw himself to the left to save one kick, and to the right to block another. And then exactly the same thing happened against Racing. Romero was so good that both shootouts finished early. Across both of them he faced a total of seven penalties and saved four of them. This is a remarkable record, capable of filling Boca with confidence for the task ahead. While scores against Palmeiras are level, the Argentines can feel as if they have a psychological lead.

Even so, coach Almiron will have plenty on his mind — not least that on Sunday, between the two legs of the Libertadores semifinal, his team take part in the world-famous Buenos Aires super-classic against River Plate. These, then, are three huge games in the course of eight days. But for all the importance of the local rivalry, it is the games against Palmeiras that offers the gateway to a title, and one that the club have been coveting for some time.

Almiron likes to switch systems and, as he works out how to marshal his resources he may well be wondering what to do with Valentin Barco, the 19-year-old starlet who has recently been linked with Premier League giants Brighton & Hove Albion and Manchester City. There are two questions here. Firstly, is Barco fully fit? He picked up an injury in the first leg against Racing on Aug. 23. Since then he has had two run outs, one of a little more than an hour, another of 45 minutes against Lanus at the weekend. Is this enough preparation ahead of what could well be the best team he has faced in his short career?

Secondly, assuming he plays, where will he be used? Barco can operate anywhere down the left flank. He has played at full-back, but this would seem unlikely against Palmeiras, where experienced Colombian Frank Fabra offers the safer option. Anyway, Barco’s virtues — his dangerous running with the ball and his whippy left foot — would surely be better employed closer to the opposing goal. So might he be used on the left wing? Or perhaps in a freer role, able to cut in and support centre-forward Edinson Cavani? Boca will surely want to make the most of Thursday’s home advantage but against the threat of the Palmeiras counter-attack they will not want to front load their team and leave themselves open.

They can, of course, rely on the work rate of Cavani. With his disposition to chase back after the move breaks down, the veteran Uruguayan remains that rare animal, a box-to-box striker. So far, though, he has just one goal for Boca. Maybe he is saving them up for the big occasion?

And so, armed with the experience of Cavani and Romero and the youth of Barco, Boca Juniors are ready to go out and do battle with the Brazilians.