IBWM's man in Buenos Aires on why South America's leading club competition is so much more than a Champions League equivalent.

May already. What's happened to the first part of the year? For most of my life – until I moved down to Argentina just over a year ago – May meant the serious onset of spring. I liked that, but I have to admit I've just said good bye to perhaps my favourite month of the year. April sees my own and a few of my friends' and family members' birthdays, but it's also the point when international club football gets really fun.

European Cup knockout stages? Not quite. They're fantastic, don't get me wrong, but there's a competition I prefer. It's more unpredictable, and more evenly matched. Perhaps overall the standard isn't as high, but in my view, it's a hell of a lot more fun. It's Copa Libertadores knockout time.

My love for the Copa started shortly after I started watching Argentine football, in 2004. I'd already visited Argentina once by then, and through my then girlfriend had become a River Plate fan. Shortly before I made my second visit, River played an epic two-legged semi-final against, of all clubs, their most hated rivals, Boca Juniors. Imagine that. All the tension of Barcelona vs Madrid, but with both legs played in front of fans who make an ear-splitting din throughout the game.

I was much less savvy with internet streaming back then, but managed to listen on the radio to the second leg as Lucho González pulled them level on aggregate at home, before a late Carlos Tevez goal looked to have put Boca through. Tevez was promptly sent off for running round behind the goal doing a chicken impression (Boca fans' derogatory nickname for River is gallinas, or 'hens'), and in stoppage time Cristian Nasuti again put River level on aggregate, 2-2. With away goals not then in use in the Libertadores (even today, ridiculously, they're not used in the final), the game went to penalties, where it also remained deadlocked until Maxi López – then a River Plate misfit, later a Barcelona misfit, and now banging them in for Catania – missed his kick, River's fifth, to send Boca through. The tie had been lost, but my love affair with the Copa had started.

A year or two later, I'd found my way around various streaming sites, and was able to watch the action as well, from afar. Some of the drama, I thought, came from the fact that I'd stay up in the dead of night, pitch blackness outside, with a silent house and a hot drink, fixated on the screen. But the stories unfolding on the pitches of South America remained compelling enough that, objectively, that can't have been the reason. After that 2004 semi-final I arrived in Buenos Aires in time to watch the second leg of the final on TV, between Boca and Colombia's Once Caldas, in Colombia. Having drawn 0-0 in La Bombonera, Once Caldas took the lead early on. Cue red-and-white (River Plate's colours) fireworks all over the area of Buenos Aires my then girlfriend's house was in. When Boca equalised in the second half, blue-and-gold ones went up. And when justice – from the River fans' perspective – was done, and Once Caldas won on penalties to prevent Boca claiming a fourth crown in five seasons, it was back to the River-coloured pyrotechnics.

The following year saw River reach the semis again, and the first of two straight all-Brazilian finals (São Paulo won the first and lost the second, in which Internacional beat them) which saw CONMEBOL pass a ruling stating that if two teams from the same nation reached the semis, they'd play each other at that stage regardless of what the draw had previously dictated. Boca, inspired by the returning Juan Román Riquelme, returned to the summit in 2007, after which their present slump began. Liga de Quito got an improbable win in 2008, thanks to a combination of a fine, free-flowing team and the altitude of their home stadium. 2009 saw Seba Verón lead Estudiantes de La Plata to a fourth title, the first since his dad Juan Ramón was banging goals in for the side four decades earlier, and last year saw Internacional once again claim the gong, just reward for being one of the continent's best-run teams over the last half decade or so.

One doesn't only remember the winners, though. Boca may have won the trophy in 2007, but the neutrals' hearts (and indeed my own, admittedly anti-Boca, one) went out to the side they beat in the semi-final, Cúcuta Deportivo of Colombia. Playing in the Copa for the first time, Cúcuta took on some of the biggest sides in the continent, and didn't just beat them, but played them off the pitch. In the first leg of their semi-final, they fell behind before roaring back to beat Boca 3-1. For the second, star striker Blas Pérez was absent, called up by Panama for the CONCACAF Gold Cup, and in fog so thick the TV cameras couldn't make out the centre circle for most of the second half, Boca ran out 3-0 winners to end the dream with a 4-3 aggregate win. Boca's vanquished opponents in the final were Grêmio, a side Cúcuta themselves had already beaten convincingly in the group stages.

Two years ago, Mexico's two remaining sides in the last sixteen left the competition amid acrimony, not on the pitch; the global swine flu epidemic led CONMEBOL (and this is cutting a very long story short) to all but kick them out for fear they might bring the disease to South America, and a compromise was eventually reached whereby both sides, San Luis and Chivas de Guadalajara, entered the 2010 edition at the same stage they'd left it the year before. Chivas went on to reach the final (losing to Inter), but San Luis, enduring drastically worse form than twelve months earlier, crashed straight out.

This year, not for the first time in recent seasons, Argentina has been poorly represented. Since Boca's glory days ended in 2007, the nation with more Copas than any other has fallen off the map, almost. Even when Estudiantes went on to win in 2009, they were the only Argentine club in the quarter-finals. This year, both they and Vélez Sarsfield are in the last sixteen, with Argentinos Juniors, Independiente and Godoy Cruz all having been eliminated in the group stage (the latter two from the same group).

In spite of the relative lack of Argentine interest, though, the Copa is as compelling as ever. After last year's tournament was complicated both by the need to include San Luis and Chivas later on (which meant not every group runner up went to the last sixteen, and made the early stages rather disjointed to follow), as well as the fact that the semis and the final weren't played until after the World Cup, this year's Copa feels much more cohesive.

With the second legs of the last sixteen being played this week, it looks for now like the most likely winners will, once again, be Brazilian; Santos, many pundits' pre-tournament favourites, have been strong but Cruzeiro, who battered Estudiantes home and away in the group stages on their way to scoring 20 goals and conceding just one in six matches, are looking like the team to beat, and take a 2-1 away win into their home leg against Once Caldas. Fluminense ought to do the job against a disspirited Libertad (of Paraguay), and for Argentina Estudiantes will be in with a chance (they drew 0-0 at home to Paraguay's Cerro Porteño last week), whilst Vélez look to be comfortably through after a 3-0 home win – or would be, if they weren't playing the second leg at the altitude of Quito. They should put Liga out, but it might end up being closer than they'd like.

 Those looking for shock results might have one already, if Universidad Católica of Chile can hang onto their surprise 2-1 away win over Grêmio. And the winners of Jaguares de Chiapas (Mexico) vs Atlético Junior (Colombia) – 1-1 in Chiapas in the first leg – will be surprise quarter-finalists. There's a decent spread of countries still represented too; eight countries have sides in the last sixteen. Trying to predict too much is never a good idea in the Copa. It's a tournament that frequently defies expectations. It's fiery, ever-changing, and more than a little bit silly. And it's fantastic to have the knockout stages back. Now if you'll excuse me, I'm off to check which midnight kick-offs it features this week...

Sam is a freelance football writer based in Buenos Aires. He edits the superb Hasta El Gol Siempre, and can be heard on the world's only Argentine football podcast, Hand of Pod.