Boca Juniors with deja vu as River Plate outflank Gustavo Alfaro's side

Before their team's home game against historic rivals Boca Juniors, three River Plate fans each held aloft a large inflatable number -- a nine, a one and a two.

It was a reference to a date: Dec. 9, 2018, when the two Buenos Aires giants met in the final of the Copa Libertadores and River won 3-1.

Oct. 1 will not be seen as a date of equal significance. This, after all, was only the first leg of the semifinal. But River's 2-0 win on Tuesday puts them right on course to make it through to this year's Copa decider.

The match was a battle of ideas. Under Gustavo Alfaro, Boca are a defence-minded team. Their best performances in the competition came in the previous two away matches. They packed the midfield, thought first about blocking their opponent and waited for the moment to strike. Both times the road to victory was paved by keeping a clean sheet -- and they also made sure they did not concede in a recent league game away to River Plate, grinding their way to a dull 0-0 draw.

River Plate coach Marcelo Gallardo was determined there would be no repeat. If Boca were to be reactive, then his side had to be proactive. They had to find a way to break down a determined defensive unit -- and the secret was width. River had clearly worked on stretching the Boca defence, on playing around and outside the back four, hitting the flanks early, switching play from one side of the field to the other. They began by swapping the flanks of their wide men. In the first half, right-footed Nico De La Cruz played on the right, and left-footed Nacho Fernandez operated on the left. It brought a quick return.

- Wright Thompson: Boca vs. River - The greatest game never played

From a throw-in, De La Cruz wriggled his way through to the byeline and squared. Keeper Esteban Andrada pushed out, and Rafael Borre was thwarted by desperate defence. With the aid of VAR, Brazilian referee Rafael Claus spotted a foul. Centre-back Carlos Izquierdoz had made a fair tackle, but coming in from the side, left-back Emanuel Mas had clearly taken Santos Borre out. After a long delay, a penalty was awarded. Borre kept his head, and as Andrada anticipated a shot to his right, the ball went high down the middle. River had an early lead, and the tone of the game had already changed.

River tried even harder to force the rhythm, to press home their advantage. Boca were still cautious, with centre-forward Ramon Abila spending most of his time in isolation. But Boca had some moments. Twice River centre-back Lucas Martinez Quarta was loose in possession and played his team in trouble -- the first time the danger was averted when keeper Franco Armani tipped over a dangerous shot from Alexis MacAllister. And once River were caught on the break after sending their defenders upfield for a set piece. Abila held the ball up superbly, and young midfielder Nico Capaldo burst forward in support -- only to lean back and balloon his shot over the bar.

It was the game's vital moment. With his tireless running, Capaldo is a symbol of Gustavo Alfaro's Boca. But neither he nor Franco Soldano, another Alfaro favourite, showed the poise to worry the defending champions.

Soldano gave way to the veteran Carlos Tevez early in the second half. Alfaro abandoned his five man midfield and went for a 4-4-1-1 in a bid to chase the key away goal. But it left them more open, and they were soon two goals down. River's second was a thing of joy - a slick passing movement down the right where full-back Gonzalo Montiel threaded in a pass and Nacho Fernandez and Matias Suarez worked a neat exchange. Always looking to work the flanks, Suarez broke right and squared low, where Fernandez arrived in front of the defence to turn in from close range.

It was time for Boca to make panicky substitutions. On came Eduardo Salvio and Mauro Zarate. But Capaldo turned an ankle and lost mobility, and Boca had used up all of their changes. Completing an unhappy evening, Capaldo was sent off late in the game -- in which River looked closer to a third than did Boca to an away goal.

River's two goal margin of victory means that the tie is well and truly alive. But Boca are going to have to come up with something special in the second leg. And Alfaro is going to have to work outside his normal cautious characteristics.

With over 900 games as a coach, he has a wealth of experience. But almost all of it has been acquired with relatively modest clubs. Some argue that he is not a good fit for a club of the size, history and pretensions of Boca -- and Tuesday's match serves as evidence for such a view. When it really matters, can he come up with something more expansive?

The stakes in the second leg, then, are very high. It could be a career defining match for Alfaro -- and he will hope that it will end with Boca fans searching for a way to commemorate Oct. 22.