Kylian Mbappe learned early on in his career that it is never wise to rule out Lionel Messi.
Two seasons ago, the France international thought he was on course to win his first European Golden Shoe. But no matter what he did, he could just not shake Messi off.
"There were days when I scored three goals and then he would score four," Mbappe later told France Football.
He even felt compelled to ask fellow Frenchman and Messi's club-mate, Ousmane Dembele, "Does he do it on purpose?!"
The Paris Saint-Germain attacker finished the season with an incredible 33 goals in just 29 Ligue 1 games, yet Messi claimed his third consecutive Golden Shoe – and sixth overall – by netting 36 times in 34 Liga outings for Barcelona.
At Camp Nou three weeks ago, though, it was Messi who had no answer to Mbappe.
The Argentine opened the scoring in Barca and PSG's eagerly awaited Champions League last-16, first-leg clash, but Mbappe responded with a stunning hat-trick as the visitors romped to a 4-1 win.
Messi will have the chance to reply in this week's return fixture at Parc des Princes, but nobody is expecting Barcelona to pull off another 'Remontada'.
The six-time Ballon d'Or winner has been looking like his old self since the turn of the year – as underlined by the fact that only Robert Lewandowski has scored more goals in 2021.
However, an extraordinary footballer is now surrounded by too many ordinary team-mates.
Messi used to be able to carry Barcelona in big games, but now he is being dragged down by them, as recent Champions League humiliations against Bayern Munich, Liverpool, Roma and Juventus have so painfully underlined.
The captain did his best to lead a defenceless Barca past PSG last month, but it was Mbappe who succeeded in inspiring an injury-ravaged team to a vital victory.
The spotlight quite rightly shone on the World Cup winner on the night of February 16. However, just 24 hours later, Mbappe was sharing it with Erling Haaland.
The Norwegian striking sensation tore Sevilla to shreds at the Ramon Sanchez Pizjuan, scoring two goals and creating another as Borussia Dortmund triumphed 3-2 in Andalusia.
Football fans already giddy with excitement having watched two budding superstars light up the last 16 on successive nights were then sent into a frenzy when Haaland told CBS Sports afterwards, "I saw Mbappe yesterday (Tuesday) and he scored some nice goals, so I got a free boost from him!"
Even if the comment was light-hearted in its nature, the idea that Haaland had been spurred on by Mbappe's exploits immediately sparked hope that the game's next great rivalry has already arrived.
Whatever one's position on the argument, nobody could deny their direct clashes made for compelling viewing. Indeed, the Clasico became must-see TV for nearly a decade because it pitted two living legends against one another.
As Messi himself told DAZN, "Competing head to head for so many years will be remembered forever. The sporting rivalry between us was very nice on a personal level. I think that the fans also enjoyed it, be they Madrid or Barca supporters, or just those who like football."
Indeed, those dramatic duels, and the rivalry they helped create, drove them on, enabling them to scale extraordinary heights. They reached one historic milestone after another as they altered fans' perception of what was possible on a football pitch.
"Messi makes me a better player," Ronaldo admitted to RMC Sport, "and vice versa. I have an excellent professional relationship with him because we have been sharing the same moment for 15 years."
We shared it with them, too, so there has been an undeniable and understandable concern in recent years that what followed the Messi and Ronaldo show would feel dreadfully anti-climactic.
They are not done yet, of course – not by a long shot. Ronaldo remains the perfect physical specimen at 36, while Messi seems invigorated by the fact that change is coming this summer, whether he stays at Camp Nou or not.
Indeed, the 33-year-old could well be revitalised by a move to a club that would provide him with the platform to win a fifth European Cup.
However, it nonetheless feels significant that there is a distinct possibility that neither Messi nor Ronaldo will feature in the quarter-finals of the Champions League for the first time since 2004-05.
Of course, while Messi's Barcelona are effectively out, few would bet against Ronaldo propelling Juventus into the last eight, given they only trail Porto by a goal (1-2) ahead of their second-leg showdown in Turin.
Indeed, it was just two years ago that Ronaldo dug the Bianconeri out of an even bigger hole with a hat-trick against Atletico Madrid that saw his side progress to the quarter-finals 3-2 on aggregate.
Interestingly enough, the night after the Portuguese forward's heroics at the Allianz Stadium, Messi was directly involved in four goals as Barcelona hammered Lyon 5-1 in Catalunya to book their place in the last eight.
A repeat performance on Wednesday night looks highly unlikely. The game is away, the French opposition is far stronger this time around, and Mbappe will be on the other side.
This feels like one of those 'changing of the guard' moments, as so perfectly illustrated by the fact that if Mbappe scores, he would usurp Messi as the youngest player in history to reach 25 Champions League goals.
Of course, even if he breaks the record, he is unlikely to have it long. At just 20 years of age, Haaland has already scored 18 goals in just 13 Champions League appearances.
He has also reached 100 career goals in just 146 games – that is quicker than Messi, Ronaldo and Mbappe. Should Haaland maintain such a ridiculous strike-rate, he would obviously end up breaking every record in the book.
Of course, what has always set Ronaldo and Messi apart from all of their would-be rivals and supposed successors, such as Neymar and Eden Hazard, is their consistency and longevity.
Sustained excellence really will be key to Haaland and Mbappe's hopes of producing a rivalry anywhere near as impressive and enthralling as that of Messi and Ronaldo.
Haaland's former Red Bull Salzburg team-mate Maximilian Wober recalled to Goal how the striker would spend his time on away trips "reading scientific articles on how he could improve his sleep pattern or diet" while the rest of the team were playing cards.
Meanwhile, Haaland's father, former Manchester City and Leeds midfielder Alf-Inge Haaland, even revealed that his son has developed a Ronaldo-inspired obsession with his diet after hearing Patrice Evra discussing the Portuguese's healthy-eating habits.
As for Mbappe, he is not a young man that lacks ambition and he has made little secret of his desire to effectively emulate his childhood hero Ronaldo by becoming the main man at Real Madrid.
If he remains fit and focused, anything is possible for the only player other than Pele to score in a World Cup final as a teenager, and it was fitting that the Brazilian legend singled him out as his most likely successor last week.
Mbappe will certainly be focused on the task at hand this week with PSG poised to eliminate bitter rivals Barcelona from the Champions League.
Of course, he knows better than most never to rule out Messi, but with the Parisians in possession of a three-goal lead, the 22-year-old should again get the better of the diminutive No.10.
Shaking off Haaland, though, could prove increasingly problematic, with the pair looking perfectly placed to dominate the game and thrill fans for years to come.
The Messi-Ronaldo show still has a few seasons to run, of course, but Mbappe versus Haaland is shaping up to be quite the spin-off.