Even at the earliest junctures of the season, the UEFA Champions League is a showcase for the world's best players on its very best days. Tuesday was no exception, this time providing a platform for a batch of players that usually play supporting roles to their headline-stealing teammates.

Paris Saint-Germain once again earned the distinction of being the Champions League's headliners, outdoing Barcelona in a 4-2 win that was the latest in a string of instant classics between two of Europe's most entertaining teams. The back-to-back champions surged to victory while relying on a wide range of talent, though they were hardly the only ones to showcase their depth. Liverpool's 4-3 win over Villarreal came courtesy of 18-year-old Rio Ngumoha, while Manchester City called upon Phil Foden in a 5-1 win over AEK Athens.

Depth will naturally be a theme of the Champions League campaign as it progresses, long seasons in store for title contenders and the teams destined for early exits. Tuesday's games offered an early glimpse at how several teams might fare down the stretch if things go according to plan – and who might throw a wrench in their plans, should the knockout phase draw put any of these teams on a collision course. Bodo/Glimt, after all, would like a word when it comes to the cute underdog narrative.

Here's what we learned from Tuesday's Champions League action.

Paris Saint-Germain's depth is actually that good

Credit to the new Champions League format: it always forces questions early in the season with high-profile matchups and these days, one question in particular: Paris Saint-Germain can't possibly keep this up, right? It was a reasonable query – Barcelona seemed as well-positioned as any to challenge the back-to-back European champions, who saw both Ousmane Dembele and Khvicha Kvaratskhelia exit the game with injuries. PSG took the lead twice, only for Barcelona to eventually find an equalizer. Things were hardly straightforward for the Parisians but by the final whistle, they had an answer to the week's most pressing question: they can, in fact, keep this up.

As Dembele and Kvaratskhelia exited the pitch, a series of teammates filled in the gaps and in a variety of ways. There was Desire Doue, who scored the game's first goal and bolstered his argument as PSG's most entertaining forward with an assist on PSG's second. Then there was the midfield trio of Vitinha, Fabian Ruiz and Joao Neves, who did the one thing that seemed most challenging – shutting down a Barcelona midfield designed to let Lamine Yamal shine. They could not keep the teen sensation at bay entirely but that was hardly a reason to stress, since each member of the trio tallied a goal contribution. Vitinha and Ruiz bagged the game's final goals, ones that finally put things out of reach for Barcelona, Vitinha's strike among the most impressive on a day of bangers. His exuberant celebration was well-earned because PSG continue to make the game's most predictable storyline endlessly entertaining.

Sure, they benefit from the fact that Ligue 1 demands less out of them than any other league in Europe asks from their top teams. Dembele and Kvaratskhelia's absences will not be felt in domestic competitions and as long as the injuries are not severe, PSG have enough to survive the league phase without them. Their teammates seem poised to handle any challenges thrown in their direction in the meantime, though, true to form for a team reimagined around a system rather than a star. Two things can be true at once: there is no reason to stop asking if someone, anyone, will slow PSG's roll sooner rather than later, much as there is no reason to stop appreciating Luis Enrique's uniquely gifted side.

Rio Ngumoha finally pops off

There are few pastimes more addicting than discovering – or rather, hoping – who the sport's next great talent might be, the friction between waiting for a player's big moment and the non-linear journey of player development always a complicating factor. The stakes were not impossibly high for Liverpool 18-year-old Rio Ngumoha on Tuesday but in a 4-3 win over Villarreal, he delivered what could be one of the first of many notable outings for the Reds. He was dynamic on the right wing, ensuring the Reds would dig themselves out of a 2-0 hole with two crucial assists, most notably on Alexis Mac Allister's go-ahead goal. He outran Sergi Cardona and made his way into the box, steady on the ball even as two defenders closed in on him. From the endline, he found a crevice of space and sent the ball to the edge of the six-yard box, making things easy for Mac Allister in the process.

Ngumoha will not solve Liverpool's defensive problems, which were on full display in the opening half hour and have hamstrung the team for a number of years. He does not need to, though – finding ways to unlock the attack will allow head coach Andoni Iraola to solve those issues slowly, as well as the conundrum around unlocking Florian Wirtz's true potential. There is never a bad time for a young player to rise up the ranks, though, and if Tuesday's outing is anything to go by, Ngumoha might be ready for the spotlight.

Phil Foden passes test

Manchester City returned to the Champions League without Erling Haaland and Antoine Semenyo on Tuesday, a favorable match against AEK Athens in front of them. In other words, it was a perfect opportunity for Phil Foden to remind head coach Enzo Maresca that he is a useful member of City's attack and he did just that with a hat trick in a 5-1 win. The context matters here – AEK Athens rank 121st in the Club Elo rankings, three spots below Belgrano, who finished 20th out of 30 in Argentina's top flight last year. A hat trick here was perhaps the bare minimum for someone like Foden to break into Maresca's lineup for bigger games and to the player's credit, he completed the task in front of him. Stiffer tests come as soon as Saturday's game at Aston Villa, which will likely be more revealing.

Bodo/Glimt are not your average underdog

Literally everything about Bodo/Glimt screams minnow. The team does not have a demonstrated history of success in European tournaments, competes in a league that rarely leaves a mark in continental contests and hails from a little-known town above the Arctic Circle. They cannot play a typical fall-to-spring season, nor can they actually host games on a grass pitch. Yet, Glimt don't fit the traditional mold of an underdog that should just be happy to compete in the Champions League. 

Before Tuesday's 4-3 loss at Napoli, they had already proven they were not to be underestimated and over the course of the game, they only affirmed that sentiment. They had an answer just about every time Napoli scored and even in defeat, they outdid the hosts – they had 2.66 expected goals from 15 shots, while Napoli had 1.52 from 17. Last week's win over Borussia Dortmund was hardly a fluke, either, Glimt's attacking outperforming the opposition's. Napoli should be allowed to breathe a sigh of relief after Tuesday's game, that win alone allowing Italian clubs to show some might after all four of them failed to win on Matchday 2. Glimt may only have three points out of nine so far but at this point, they are good enough to target a spot in the knockouts and with the likes of Lille, LASK and Lens up next, they might be able to pull it off.

Sergino Dest's rare display

Sergino Dest's strengths and weaknesses are unmistakably easy to categorize – he's a wingback who genuinely prefers the attacking aspects of the job, defensive responsibilities be damned. His skillset is so specific that U.S. men's national team head coach Mauricio Pochettino intentionally utilized him as a more traditional winger during the World Cup, a decision Dest only reinforced with a poor defensive outing in the round of 16 loss to Belgium. The PSV player, though, loves a highlight-reel-worthy moment and delivered just that in a 1-0 win over Porto, one that allowed him to showcase his defensive instincts for once. He came up with a goal-saving clearance late in the game, preserving PSV's narrow win in the process. Dest was also in need of a strong moment for an American audience, failing to impress over the course of the prolonged fall international break headlined by a group of up-and-coming talents.