The 2018 CONMEBOL Copa Libertadores has reached its semifinal stage featuring traditional powers from the two biggest football countries in South America. River Plate will host defending champions Grêmio in the first leg of the first semifinal on Tuesday night; Boca Juniors will open the second semifinal at home to Palmeiras on Wednesday. Even though Brazilian and Argentine clubs have appeared in the Libertadores semifinals more than any other CONMEBOL country (71 appearances for Argentina among 12 clubs, 60 appearances for Brazil among 15 clubs), this year marks the first time since the Libertadores went to a knockout format that the semifinal is comprised entirely of clubs from those two countries.

In this post, I’ll preview the semifinal ties with some assistance from DataFactory match data.

River Plate vs Grêmio

River Plate come into this semifinal having had their record unbeaten streak — 32 matches across all competitions — broken by Colón 1-0 in Santa Fe last Friday. Grêmio drew 1-1 at América (Minas Gerais) last Saturday. Neither team is at the top of its respective domestic league, and it’s worth remembering that River qualified for this year’s Libertadores through the Copa Argentina and not their Superliga performance. Grêmio have made the Copa Libertadores their own fiefdom over the last two seasons, they won last year’s competition with a string of dominant performances, and they have duplicated that effort this year.

Grêmio are, on paper and on the field, the best team left in the competition. They have scored more goals and allowed the second fewest, and they have generated 2.17 xG/90 and allowed 0.71 xGA/90 for a +1.46 expected goal difference. They create a lot of chances through Cicero, Ramiro, and Maicon, put away those chances through Jael or Everton, and are very solid in the back with Kannemann and Geromel as center backs and Grohe in goal. With the pairing of Kannemann and Geromel on the pitch, Grêmio have kept clean sheets in 19 of the 34 knockout matches that they played. In fact, they have only allowed more than one goal in an elimination round match before: two in the first leg against Estudiantes in the round of 16. Grêmio can win matches in a variety of ways: either a deep and compact stance that cedes more of the possession to the opposition before launching counters from the wings, or by dominating possession, controlling the center of the field, and circulating the ball to their targets up front.

River Plate will have to hang their Libertadores hopes on their defensive ability, just as they have had to do in the Superliga. Of the Libertadores teams who have played ten matches, River — along with Grêmio and Independiente — are the only sides to have allowed fewer than 1.0 xGA/90. In addition to Palmeiras and Independiente, River have yet to allow a goal from a set piece. Their forward line has not been as potent as the other semifinalists, however. Ignacio Scocco and Rafael Borré are likely to start up front, but they have scored just three goals between them in this year’s Libertadores. Lucas Pratto, who has the third-highest xG/90 on the squad, is likely to enter the match as a substitute. Juan Fernando Quintero and Gonzalo “Pity” Martínez will play in midfield but will attempt to create numerical advantages in support of Scocco or Borré. The linchpin of River’s play, as he has been on so many occasions, will be Leonardo Ponzio at holding midfield. The outcome of his play against Maicon will go a long way toward determining the outcome of the first leg and ultimately the tie.

River will have to take the initiative in Tuesday’s match, a situation that Grêmio will be more than happy to accommodate, but they will need a greater contribution from Quintero and the forward pairing than they have been able to provide in this tournament. A goal by the Tricolor will almost certainly decide the tie. I expect that Grêmio will ultimately win the tie, and they just might win both legs.

Boca Juniors vs Palmeiras

This tie features two teams that have been at the top of their respective domestic leagues in recent years. Boca have been champions of Argentina over the last two seasons, while Palmeiras have won two of the last three Série A titles. Boca come into this tie having drawn 0-0 with Rosario Central last Saturday, while Palmeiras defeated Ceará 2-1 — both sides playing second-string squads as expected.

This is the more evenly matched of the two semifinal series. Boca Juniors have generated 1.63 xG/90 (0.85 open play/0.63 set play/0.14 penalty) and allowed 1.07 xG/90 (0.63/0.32/0.12), while Palmeiras generated 1.62 xG/90 (1.01/0.54/0.06) and allowed 1.06 xG/90 (0.45/0.45/0.17). The difference is that Palmeiras have allowed just four goals (not counting own-goals) in the Libertadores compared to Boca’s seven, and Palmeiras have the best shot conversion rate of the Libertadores sides to have played ten matches.

In my view, the two principal figures for Palmeiras are Miguel Borja and Moisés. With nine goals scored (and just one from a penalty), Borja will almost certainly finish as Libertadores top scorer, and he is two goals away from matching Tupazinho’s record for Palmeiras in the 1968 Libertadores. Borja could also join the elite group of Libertadores winners with multiple clubs (he won the Libertadores with Atlético Nacional in 2016). Moisés plays in the center of the Palmeiras midfield and serves as the primary link between their defensive midfielders (usually Bruno Henrique and Felipe Melo) and Borja.

Boca have tended to play somewhat wide from a four-man back line, with their backs Lucas Olaza and Leonardo Jara making contributions in circulating the ball to their attack. The decisive players in Boca’s play will be Pablo Pérez in the center of the park and Cristian Pavón up front. As in the other semifinal, the duel between Moisés and Pérez could have a significant impact on the destiny of the semifinal tie. Darío Benedetto was the best player in the Superliga until his ACL injury last year; he might get a run in the first leg but I doubt that he will have a significant impact on the match.

This tie also features a test of two managers. Guillermo Barros Schelotto (who just might be a target of several MLS clubs, including Atlanta United) has won the top flight with the best teams in Argentina, but he does not have a solid record in the big matches against evenly matched rivals. Luiz Felipe Scolari — Big Phil — makes his return to South American football’s biggest stage, but the last memory many fans outside of South America have of him was at the 7-1 rout of Brazil at the 2014 FIFA World Cup. He does have a defensive pedigree, though, and he has won the competition before with Grêmio (and Palmeiras in 1999).

It will be a fascinating tie, and one with a narrower finish than the other semifinal. I believe Boca will end up winning narrowly and possibly via penalties.