BARCELONA -- Three quick thoughts from the Camp Nou as Barcelona cruised to a 3-0 win Tuesday over Juventus in the Champions League group stage on matchday one.

1. Barca win clash of European heavyweights

Lionel Messi (who else?) was the maestro as Barcelona exacted some revenge for last season's Champions League elimination at the hands of Juventus. Barcelona failed to score in either of their two games against the Serie A champions last April, but Juve coach Massimiliano Allegri predicted it would be astonishing if they failed to score again at Camp Nou on Tuesday. He was right.

The Catalan giants didn't score just one, either, but three as Messi led coach Ernesto Valverde's improving side to a win that suggests we can hit the pause button on any imminent thoughts of a decline in the post-Neymar era.

The first goal came on the stroke of half-time and began with Barca goalkeeper Marc-Andre ter Stegen. Ousmane Dembele (making his full debut) and Luis Suarez were also involved, but it was mainly about Messi. Juve goalkeeper Gianluigi Buffon glanced to his left but knew immediately there was no point in diving when the Argentina international let fly with his first touch in the Juve box off the half-volley. A millisecond later, the ball struck the inside netting. Messi then set up the second after the break, as his half-cleared cross was driven home by Ivan Rakitic. Messi scored his second (Barca's third) with another stunning effort. Drifting in past two defenders from the right, he sent Buffon the wrong way and lethally cut the ball into the reverse corner.

This game was billed as a matchup between two of Europe's best teams. And they are -- still. But, due to a number of circumstances, there had been uncertainty about both teams throughout the summer. Both were out to make a statement to their doubters here, but Barca took control from the start.

Barcelona's Andres Iniesta, starting his fourth game in little over a week, shimmered. Dembele, starting on the right, and Nelson Semedo behind him also looked bright early on. Between them, they will break a lot of hearts on that flank this season, but there was little cutting edge initially and Juve looked comfortable. In fact, the Serie A champions had the game's best moments. Mattia De Sciglio's long-range effort drew a fine fingertip save from ter Stegen. More routine saves followed to deny Paulo Dybala and Miralem Pjanic, while Barcelona's Jordi Alba blocked Rodrigo Bentancur's effort.

Buffon flexed his muscles at the other end, too. After Messi's free kick came back off the wall, the Italy goalkeeper produced a stunning reflex save to deny Suarez, but then Messi broke the deadlock and everything changed. Barca had more space in the second half against a Juve side that were inclined to attack. They had more fun, too.

With the score neatly poised at 1-0, Dybala had Juve's best chance, but he blazed over the crossbar, unmarked from the edge of the box. Then, when his compatriot Messi (who had just hit the post himself) set up Barca's second goal at the other end, you got the feeling this one was over.

There was still time for Suarez to have a fourth goal ruled out for offside, while ter Stegen was called into action several more times and Gerard Pique cleared off the line, but Juve were playing for pride by that time, not the points.

Messi was superb in attack, scoring twice and guiding Barca to a much-needed victory over visiting Juve. Alex Caparros/Getty Images

2. Mesmerising Messi in fine form

It's a point that's been made many, many times but is always worth remaking: When Messi is at his best, Barca are pretty good.

His role has changed this season, and it looks to be to devastating effect. Valverde, as he suggested when unveiled as Barca's boss in May, has shifted his playmaker in from the wing. To Messi's right, Valverde has deployed Dembele, ably backed up by Semedo. To Messi's left, although more as an inside-forward than a winger, is Suarez. Alba is free to eat up the rest of the space on the left flank.

So far, the shift has contributed to an even more purposeful Messi. Somehow, he didn't score in the opening La Liga game of the season against Real Betis, although he did batter the woodwork three times. Since then, though, he's scored two goals against Alaves, three against Espanyol and now two against Juve. Both his goals against the Italians were typical Messi. His first came after a one-two with Suarez, and his second looked easy as Messi beat two Juve defenders. He also set up Rakitic's goal and hit the post.

While Barca's summer was plagued by player exits (Neymar's in particular), speculation, failed signings, and a coup attempt against the board, Messi has kept quiet. He has agreed to a new contract with the club but has yet to sign the deal officially. For the moment, he's doing his talking on the pitch, but the board, under pressure, desperately needs him to smile for the camera and put pen to contract paper soon.

Paulo Dybala, right, was wasteful as Juve struggled to get back into the game after Messi's opening goal. VI Images/Getty Images

3. No panic alarm for Juve despite result

As much as Valverde won't let this Barca win go to his players' heads, Allegri will also look to ensure that Juve move on from it quickly and don't linger on the emphatic defeat.

Ultimately, there were extenuating circumstances for Juve. For starters, Giorgio Chiellini, Sami Khedira, Mario Mandzukic, Benedikt Howedes and Claudio Marchisio were all missing through injury. On top of that, Juan Cuadrado was suspended, and right-back De Sciglio was forced off with an injury in the first half, leaving Allegri with a very mismatched side.

Despite that, they had their moments, especially in the first half. Dybala looked a bit distant, but Gonzalo Higuain linked play well and Douglas Costa was a threat. Behind them, Pjanic patrolled the midfield well and questions were regularly asked of ter Stegen. Even after falling, one, two and subsequently three goals behind, the Old Lady still created plenty of problems.

Juve will back themselves to have too much for Olympiacos and Sporting Club in their upcoming group games, while they'll also fancy their chances at home to Barca. After all, it's only been barely half a year since Juventus so convincingly beat the Blaugrana en route to the final.