Copa Libertadores: Flamengo gamble ahead of Gremio; River Plate faves over Boca

Flamengo took a risk to play a full strength squad ahead of their crucial match vs. Gremio. NELSON ALMEIDA/AFP via Getty Images

The final of last year's Copa Libertadores caught the attention with its chaos and controversy -- fan violence meant that the decisive second leg between Buenos Aires rivals River Plate and Boca Juniors was switched to Madrid.

This year's version may hit the headlines for more palatable reasons. This week will sort out the finalists of what is proving the most intriguing Libertadores for years -- the result of a blend between the old and the new.

The old is represented by River and Boca, whose rivalry this time takes place in the semifinals. And in the all-Brazilian semi there is the continued excellence of 2017 champions Gremio, through to this stage for the third consecutive year.

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And then there is the new -- Flamengo of Rio, who since appointing Portuguese coach Jorge Jesus in the middle of the year have swept all before them in a swashbuckling, eye catching manner.

Of the four semifinalists, Flamengo were the only not to field a reserve team in the weekend's domestic matches. A 2-0 win over local rivals Fluminense carries them a full 10 points clear at the top of the Brazilian league with eleven rounds to play. It would be a big surprise if they were to let the league title slip away.

But have they already let the Libertadores slip away? That is the hope of Gremio coach Renato Portaluppi. Three weeks ago, in front of their own fans in Porto Alegre, Gremio spent the first 45 minutes barely able to get out of their own half.

"We never even saw the ball," confessed their coach.

This is extraordinary. Gremio are a possession based side. But they were starved of all possession. Flamengo strangled them in their own half. With a high defensive line, an all action midfield and a fluid attack, Flamengo were irresistible. Before the interval they had over 70% of possession.

The second half was more even. Nevertheless, Gremio knew they were lucky to get away with a 1-1 draw. Flamengo had three goals disallowed. 4-1 would have been a fair summing up of the game. Gremio hope, then, that Flamengo have missed their big opportunity. They could have killed the tie off in Porto Alegre. But Gremio are still alive and dreaming going into Wednesday night's second leg at the Maracana.

But Gremio have problems of their own. Crucial to their strategy is left winger Everton, their leading attacking weapon. Slipped behind the Flamengo defence, he could cause all sorts of problems. But who will do the slipping? Gremio have two fine playmakers capable of supplying the killer pass -- 2017 hero Luan and the highly promising Jean Pyerre. Both are struggling for fitness. Neither are seen as likely starters.

Flamengo, meanwhile, may be paying a price for the option of their coach to play all of the matches as close to full strength as possible. Former Bayern Munich right back Rafinha and Uruguayan playmaker Giorgian De Arrascaeta have picked up injuries, and may not be fully fit in time. But the squad has depth, and the team has momentum. After 17 games without defeat confidence is high and the club's giant support is living a moment of ecstasy. Gremio will probably have to produce the finest night in their three year period of success if they are to reach the final.

Twenty four hours earlier, Boca Juniors will have to come up with something special to overturn the 2-0 lead built up in the first leg by River Plate.

Three weeks ago they went down to tame defeat. It was argument for those who feel that coach Gustavo Alfaro is not a good fit. Almost all of his long career has been spent in charge of small clubs. He has a cautious mentality. But caution will not save Boca now. They must impose themselves on the game -- against dangerous opponents who have the away goals rule in their favour. If River score one, Boca will need four. Can Alfaro build a team for this task? It looks like a career defining night.

He is clearly keen to involve the veteran Carlos Tevez in the action, probably from the kick-off. Alfaro has been looking at different schemes, even considering a switch to back three to enable him to have width plus Tevez operating behind centre forward Ramon Abila. It would seem, though, that 4-2-3-1 is more likely -- with River set to stay in the 4-1-3-2 of the first leg. Can Boca get behind the River front five, and can they do it without leaving themselves open to the counter attack? And can they do it for the full 90 minutes?

River have a strong bench, with striker Ignacio Scocco in form and Colombian playmaker Juan Fernando Quintero playing his merry way back to fitness. Boca's fans in the Bombonera stadium will be up for carrying their heroes to a night of heroics. But River are favourites to get through and defend their title.