On paper, this was this round's clash of the titans, Paris Saint-Germain (PSG), the biggest and most successful team in France, versus La Liga titans Barcelona. In practice, it started like a sparring match and ended like a massacre.

The opening passage was fascinating, not in and of itself but what it showed about each side's respective league. One thing that's striking is how tactically lose both PSG and Barcelona began; they're obviously so used to being the big boys of their divisions that they don't have to adhere to traditional formations and set-ups.

According to Transfermarkt, both sides were officially 4-3-3. In the Spanish, it was practically imperceptible, for the French they snapped into it when pressing forward - particularly noticeable when the front three of Kylian Mbappe, Mauro Icardi, and Moise Kean made an attack - but it still didn't feel especially intentional and made the game feel toothless.

Antoine Griezmann tried out his long sprints, Marco Verratti and Idrisa Gueye alternated passing triangles with their opposites Pedri and Frenkie de Jong and, in what seemed like a bad omen, and main man Messi tested space in preparation for a later attack.

It started to switch when Barcelona got a penalty. Messi passed the ball into the box with the exact parabola as a throw from Tampa Bay Buccaneers quarterback Tom Brady, but de Jong got tripped by Layvin Kurzawa and won the foul. In all the replays, it seemed at best accidental and, at worst de Jong intentionally clipping his own heels to draw the penalty.

Messi converted effortlessly in the 27th minute, and this spurred PSG into life. What new manager Mauricio Pochettino has actually done to the French champions isn't clear in regards to playing style, he has, however, definitely begun to instill a more mature mentality into the side.

In last season's Champions League final, PSG crumbled when they went 1-0 down to Bayern Munich. Four years ago, PSG infamously faced Barcelona at the Camp Nou with a 4-0 first-leg advantage and somehow managed to lose 6-1. This time, instead of bursting into tears after getting their noses bloodied, they bit down on their gum shield and knew they were in a fight.

Five minutes later, PSG stormed down the pitch and completely outclassed Barcelona in making it 1-1. Marquinhos sent it long diagonally to Kurzawa on the left. He volleyed it back in to Verratti. He knocked it town to Mbappe, who then danced around Clement Lenglet and smashed it beyond goalkeeper Marc-Andre Ter Stegen.

This set the tempo for the remainder of the game. Barcelona's spine of Messi, Sergio Busquets, and Gerard Pique has a combined age of 99, and it took until they scored for PSG to realize this. From here, they literally and figuratively ran rings around the aging Catalans.

The assault on Barcelona's goal began early in the second half. Several attempts were saved or deflected until the 65th minute when Pique, too slow, too clumsy to be playing center-back against a squad this pacy, defended a cross from Alessandro Florenzi straight into the feet of Mbappe. 2-1.

Kean made it 3-1 five minutes later by speeding into a gap in the Barcelona line as they defended a free-kick. Mbappe got his hat-trick in the 85th; Julian Draxler subbed on for Verratti, and himself broke on a counter and, just outside the Barcelona box, linked up for an elegantly simple goal. His pass to Mbappe was perfectly weighted; Mbappe's finish was pure finesse.

The game ended 4-1 to PSG. There's been no mention of Barcelona in the second half because they were present in body yet absent in mind and soul. Griezmann was their man of the match by virtue of occasionally trying to attack, however, everything he tried was a solo effort; that may work when you play Eibar and Deportivo week-to-week, you can't be a hero in the Champions League. Their star, judging by how often UEFA's director got cameras on him, was Pique; one of the defining images of the game will be the myriad Sergio Leone-esque close-ups of him looking perplexed as PSG do laps around him.

When Barcelona were smashed 8-2 by Bayern Munich in last year's tournament, it was considered the definitive end of an era and triggered the ongoing drama in the team: Luis Suarez left, club president Josep Bartomeu left, Messi tried to leave, etc. And yet, here they are, no lessons have been learned. They are still reliant on the players and tactics that ruled the world a decade ago, unaware the game has moved on and left them behind.

(Header: Paris Saint-Germain's Kylian Mbappe scores the final goal of his hat-trick during his team's 4-1 win over FC Barcelona in the Champions League Round of 16 at the Cap Nou, Barcelona, Spain, February 16, 2021. /AFP)