3 takeaways from Wednesday's Champions League action

On the heels of Tuesday's action-packed slate of Champions League group stage openers, Wednesday's clashes followed suit in terms of excitement.

Juventus struggled, Lyon made quick work of Dinamo Zagreb (with 12 of Les Gones' last 18 continental goals coming against the Croats), and Monaco stunned Tottenham at its makeshift Wembley Stadium digs.

With that in mind, here's a look at four takeaways from Wednesday's matches:

Borussia Dortmund: The kids are alright

When 2012-13 Champions League runner-up Borussia Dortmund bid adieu to Henrikh Mkhitaryan, Mats Hummels, Ilkay Gundogan, and Jakub Blaszczykowski, gaffer Thomas Tuchel ushered in a youth movement, and, at the same time, put his imprint on a club that still had Jurgen Klopp's signature on it.

When Tuchel's lot traveled to Poland to mark Legia Warsaw's return to the group stage after a two-decade hiatus, the German gaffer was faced with a squad selection conundrum that most managers would kill for. With players of the pedigree of Shinji Kagawa, Matthias Ginter, and Sebastian Rode looking on from the bench, Tuchel fielded a starting XI with an average age of 24.25 years.

While a trip to Poland's capital is hardly a date with Bayern Munich at the Allianz, Dortmund started proceedings with an absolutely stunning display, and it was a young core that featured Julian Weigl (21), Ousmane Dembele (19), Christian Pulisic (17), Mario Gotze (24), and defender-cum-midfielder Raphael Guerreiro (22) who were the stars.

A treble of tallies in the opening 17 minutes was enough to cement a result that was hardly in doubt, with Dembele exhibiting his versatility in notching two assists for the visitors, while teenager American Pulisic played provider for Gonzalo Castro's 76th-minute goal.

Ilkay Gundogan: A dazzling debut

Manchester City summer signing Ilkay Gundogan was handed his debut against Borussia Monchengladbach, and the former Dortmund stud didn't disappoint.

Starting alongside Fernandinho in David Silva's stead, the 16-time capped German displayed an aggressive opening half in a box-to-box role before coming off in the 81st minute for Gael Clichy.

Pep Guardiola immediately embraced his €27-million man on the touchline as the Etihad faithful serenaded him with cheers, and for good reason. Gundogan, 25, completed 89 percent of his passes, completing 51 of those paired with three successful dribbles. The excess of riches at Guardiola's disposal is almost unfair, as another newcomer, Leroy Sane, provided an incisive assist on Kelechi Iheanacho's nightcap.

Some take time to acclimate to a new club, while others, like Gundogan, hit the ground running. From the looks of it, the midfielder fits perfectly into City's system.

Guardiola is now the first Man City boss to win his first seven matches. Not too shabby that.

Real Madrid: Win when you're crap

When Sporting's Bruno Cesar scored two minutes after the interval, host Real Madrid faced losing at the Santiago Bernabeu in Champions League play for the first time since a 4-3 last-16 defeat to Schalke on March 10, 2015. In that instance, Los Blancos ended up winning 5-4 on aggregate on its way to lifting a record 11th title.

Related - Watch: Sporting's Cesar stuns Real Madrid with opportunistic finish

A stodgy opening half gave way to slightly more optimism in the second, as the host began to assume its typical dominant form. Yet still, there was something amiss, and a front three of Cristiano Ronaldo, Gareth Bale, and Karim Benzema were hardly a lethal prospect.

For the umpteenth time, Ronaldo was the hero, curling in a trademark free-kick to offer Zinedine Zidane's lot hope in the 89th minute against his former side. Game on.

Related - Watch: Ronaldo finally scores a free-kick, doesn't celebrate vs. Sporting

Substitute Alvaro Morata turned Sporting's day from bad to worse, handing Real a late victory courtesy of a 94th-minute goal. Tough luck for Sporting, who put together an organised and astute display against the defending champ only to lose in the final moments. Such is football.

Goal of the Day: Bernardo Silva

Tottenham hasn't won any of its last five fixtures at Wembley Stadium, and Monaco winger Bernardo Silva ensured that streak of futility continued when he bagged this stunning first-half opener. Ben Davies, what are you even doing out there?