The Champions League returned with some titanic clashes as the new-look league system got into full flow.

Here are the five biggest talking points from all of the action in Europe.

Arsenal look the real deal

The tie of the evening put unbeaten sides Arsenal and Paris Saint Germain against one another in north London, and Arsenal provided yet more evidence that they may well be the real deal this season.

They raced into a 2-0 first half lead courtesy of goals from Kai Havertz and Bukayo Saka, before dropping deep into a more compact shape in the second half to ensure that they kept their clean sheet intact.

Meanwhile, the French giants had just two shots on target, both of which were held comfortably by David Raya.

📸 ADRIAN DENNIS – AFP or licensors

It was the first time that PSG have failed to score in 51 Champions League group/league stage games, suggesting that Arsenal may finally have added some steel to their attractive attacking football.

Could this be the season they finally end the campaign with some silverware to show for it?

Brest aren’t here to make up the numbers

After coming third last season in France, Brest entered the Champions League for the first time and have already made a splash.

They followed up a 2-1 win over Sturm Graz on Matchday One with a 4-0 thrashing of fellow Austrian side RB Salzburg to briefly move to the top of the new look Champions League table.

Games against Spanish giants Real Madrid and Barcelona as well as German champions Bayer Leverkusen are still to come for the French underdogs, but they also face Sparta Prague, PSV and Shakhtar Donetsk.

A couple more strong performances will put them in a great position to qualify for the next stage.

Karim Adeyemi could be the next star in Dortmund

Borussia Dortmund have a strong reputation for developing talent, with constant speculation about who the next cab off the rank could be.

If tonight is anything to go by, it could be speedy wide man Karim Adeyemi, who announced himself to Europe with a first half hat-trick against Celtic to put his side in control.

He has suffered a tough start to the season, but his talent has never been in doubt and his consistency has always been what is required. He showed a glimpse of just how good he could be against Celtic.

With just three shots on target totalling 0.24 expected goals, he walked down the tunnel with the match ball already secured at the interval, and will be hoping that his hamstring injury is less severe than it seemed.

Meanwhile, Celtic fans may want to look away!

Leverkusen march on

Though they missed out on a historic treble last season by losing in the Europa League final against Atalanta, Xabi Alonso’s Leverkusen are proving that it was no fluke campaign under the Spaniard.

A goal from Victor Boniface meant that they edged past Milan in the Bay Arena to make it two wins from two and move up to third in the early running, with a clash against second-placed Brest to come next time out.

The German side have already surrendered their unbeaten status this season, but are showing that the step back up to the Champions League is no problem at all.

With tough games against Liverpool, Inter and Atletico Madrid still to come, they will be very grateful to have banked maximum points in their hunt for a spot in the knockout rounds.

The new Champions League format guarantees goals

There was plenty of speculation when the new-look Champions League was announced, with many fearing that it would ruin the competition.

But it hasn’t done anything to stop goals yet, which will come as a relief to league stage sceptics.

Across the nine games that took place on Tuesday, there were a mammoth 32 goals, adding to the 57 that were scored in the first round of matches.

They may not all be particularly close ties (many of today’s goals came in a 7-1, 5-1 and three 4-0 scorelines), but there is certainly more jeopardy than the old group stages, and unlike the group stage it is likely to stay that way right until the final kick of a ball.