4 takeaways from Tuesday's Champions League action

The first Champions League matchday delivered a balance of blowouts, tactical malpractice, and individual brilliance. It's early in the 2016-17 campaign, but it's already offered clues as to whether some teams are title favourites or pretenders.

Here are four takeaways from Tuesday's contests:

Arsenal a big mess in Paris

Before Arsenal even stepped foot on the pitch, it looked beaten. Arsene Wenger's decision to play David Ospina ahead of Petr Cech drew the most attention, but starting Francis Coquelin and Santi Cazorla in a midfield two was what stunted the Gunners.

In fact, Ospina made several saves to keep Arsenal in the match.

The problem was clearly in the middle of the park. Keeping Granit Xhaka on the bench was a head scratcher, and so was playing a high line. Arsenal's midfielders were forced into mistakes, and sloppy in possession.

Without much pressure on the ball, Marco Verratti was also able to loop passes into vacant areas. There was so much open field for PSG to exploit, and if it wasn't for Edinson Cavani's profligacy, the host would've run away with the contest.

Alexis Sanchez as a striker is a similar concern. It was only after Olivier Giroud emerged from the substitutes' bench that Sanchez contributed his best stuff. Free to play in from behind, the Chilean scored the equaliser without anyone tracking his run. It's a much better plan than launching speculative crosses to someone who's only 5-foot-6.

Barcelona having fun again

There's nothing like a Champions League night at the Camp Nou to kick start a campaign.

Barcelona was a shell of itself as it dropped three points to newly promoted Alaves on the weekend. Lionel Messi, Andres Iniesta, and Luis Suarez were all rested from the start.

But all three scored Tuesday in a 7-0 hammering of Celtic, with Neymar getting involved in five of the goals. It was a reminder that a full-strength Barcelona side is still something to behold.

This one was a vintage performance. Messi popped the earliest of his 86 Champions League goals in the third minute, finished off a 19-pass move to extend the lead, and tapped in a second-half marker to complete the hat trick.

He now has six Champions League trebles - one more than eternal rival Cristiano Ronaldo.

Oblak showing he belongs in elite class

Jan Oblak made a crucial penalty save to preserve Atletico Madrid's 1-0 win over PSV, an encouraging sight for a goalkeeper who's only downfall is spot-kicks.

The Slovenian has all the attributes to be considered a world-class netminder - reflexes, distribution, and courage - and it now looks like he can handle big moments from 12 yards.

His heroics against Bayern Munich in last season's Champions League semi-final showed how reliable he can be, but there were questions during the shootout in the final. Real Madrid scored all five spot-kicks with relative ease to claim the Undecima in Milan.

The critics may now have to reconsider their accusations after this performance. Oblak is still only 23 years old, and he's learning on the go.

Milik proving poacher credentials

Many wondered if Arkadiusz Milik was not only worth €35 million, but even a worthy successor to Gonzalo Higuain.

We have early answers: yes, and yes.

The Poland international has made a habit of scoring in bunches for his new club, heading in three of his four goals for Napoli. His brace against Dynamo Kyiv handed the visiting Partenopei a 2-1 comeback win, and if it wasn't pretty, it was opportunistic.

His other two goals came in a dominant 4-2 win over AC Milan.

Milik prompted concerns about his finishing during Euro 2016, when he missed an open net.

But both his goals against Kyiv show he has the instinct to put himself in scoring positions.

Goal of the Day: Andres Iniesta

Iniesta reminded the masses of his brilliance as excerpts of his new book were released in recent weeks. But Tuesday's pitch-perfect volley against Celtic was concrete evidence of his exquisite touch and ability.