When the cliched term 'it's men against boys' is used in football, it's rare for the 'men' to be an up-and-coming side finding their feet and for the 'boys' to be multi-time champions of Europe.
Okay sure, Barcelona are hardly an underdog in any situation and most of their young blood featured from the bench in this encounter in question, but this is a team in rebuild and one that seemed destined to miss out on a top-four finish mere months ago.
Xavi's side tormented that of Carlo Ancelotti's in Sunday's Clasico and secured a seismic 4-0 win, a defeat of infamy handed to their biggest rivals.
Real Madrid had their fair share of momentum coming into the match in spite of Karim Benzema's absence - their lead at the top of La Liga looks unassailable, they're still buoyant from their Champions League triumph over PSG and are looking forward at the chance to exact revenge on Chelsea in the next round.
But Los Blancos have come crashing back to Earth and their worst fears have been realised - Barcelona are coming back. The club that looked destined to fall by the wayside several times in the last couple of years, the team that had Lionel Messi forcibly taken away from them, that is relying on a near-rookie coach to save them from total oblivion, are on their way up again.
In the short-term, it's fine. Real Madrid are still going to walk to the league title and while they'll probably fall short in the Champions League, at least Barça won't be the ones beating them to it. But they're cooking something interesting over at Camp Nou and Florentino Perez and co should be concerned.
The match may have been different had Benzema been fit, but his 34-year-old presence alone won't have completely flipped a switch and it won't do much in the long-term future of this rivalry.
It's for these reasons that signing Kylian Mbappe this summer is an absolute must - not just for Real's own ventures, but to keep Barcelona's progress at arm's length.
At this current rate, Xavi's charges will be competing for major honours next season and there's not a lot Real can do to combat that short of triggering the release clause of every Blaugrana player on deadline day. They need to focus on their own rebuild, begin shifting the old guard (who looked very, very old on Sunday) out and building around a player who has a pretty decent shout of winning several Ballons d'Or in the 2020s.
It seems inevitable that Mbappe will sign for Real this summer anyway, but Sunday was a wake-up call that he can't just be the face of a Bernabeu evolution, he needs to be it of a revolution to rival Barcelona's.