Kylian Mbappé and Erling Haaland took their high-flying scoring acts into Europe as the Champions League returned, while last season's standout star Karim Benzema limped off with an injury after less than 30 minutes. (More Football News)

Mbappé and Haaland both netted two goals as their respective clubs Paris Saint Germain and Manchester City began their European campaigns with victories, underlining just why those two teams are again among the favorites for the title.

Real Madrid's chances of defending its crown probably depend largely on having a fully fit Benzema, but the France forward had to come off with an apparent knee injury in the 30th minute against Celtic. Second-half goals from Vinícius Júnior, Luka Modric and Eden Hazard still secured a 3-0 win for the Spanish giant in Glasgow.

Benzema was in a league of his own in the competition last season, netting 15 goals in 12 games to lead Madrid to the title. But Mbappé and Haaland look ready to challenge the Frenchman for the status of Europe's top striker as they try to lead their clubs to an elusive first Champions League title.

The 23-year-old Mbappé, who has seven goals in five league games so far, scored his double in the first 22 minutes of a 2-1 home win over Juventus to become the youngest player to reach 35 goals in the competition — beating the mark held by teammate Lionel Messi.

The 22-year-old Haaland has 25 goals in 20 Champions League games — also a record — after scoring once in each half of Man City's 4-0 win at Sevilla. The Norway striker, who has 10 goals in six Premier League games this season, has now netted on his Champions League debut for three clubs — Salzburg, Borussia Dortmund and City.

Also, Dinamo Zagreb upset Chelsea 1-0 at home while Serie A champion AC Milan was held to a 1-1 draw at Salzburg.

MBAPPé SINKS JUVE

Mbappé's opening goal for PSG came after just five minutes following some audacious link-up play from Neymar.

Mbappé played a short pass to the Brazilian before making a run into the area, with Neymar holding onto the ball just long enough before chipping it over a defender and into the path of the France striker, who volleyed it first-time past goalkeeper Mattia Perin.

The second came after he exchanged passes with Achraf Hakimi and beat Perin with another first-time finish. United States midfielder Weston McKennie pulled one back for Juventus in the 53rd, creating a tense finale in Paris.

In the other Group H match, Benfica defeated Maccabi Haifa 2-0.

CHELSEA STRUGGLES

Pierre-Emerick Aubameyang couldn't give Chelsea's stuttering attack any kind of instant spark as the Blues failed to impress once again following an inconsistent start to the season.

Aubameyang made his Chelsea debut after his move from Barcelona, playing with a face mask to protect his injured jaw, and had one goal ruled out for offside while his teammates repeatedly failed to beat goalkeeper Dominik Livakovic.

Instead it was Mislav Or?ic who continued his scoring streak against English teams, racing away from Wesley Fofana — another of Chelsea's marquee signings — to score on a breakaway in the 13th minute.

"It's an underperformance from us,” said Chelsea manager Thomas Tuchel, whose team has lost twice in the Premier League already. “We are clearly not there where we need to be. …. At the moment everything is missing.”

Noah Okafor put Salzburg ahead against Milan near the half-hour mark by shooting through the legs of goalkeeper Mike Maignan, but Alexis Saelemaekers equalized before the break.

Rafael Le?o then nearly won it for Milan in stoppage time when he had a shot deflected off the post.

U.S. international Sergi?o Dest came on in the 57th minute for his Milan debut following his transfer last week from Barcelona, one of six Americans in action on the night.

CITY ROLLS IN SPAIN

Haaland could well be the piece that Man City has been missing as it repeatedly came up short in Europe under Pep Guardiola.

The Norwegian again showed his uncanny ability to be in the right place at the right time as he was on hand to steer in a cross from Kevin De Bruyne in the 21st minute and then tapped in a rebound for the third goal in the 67th. Phil Foden and Ruben Dias scored the other goals for City in a dominant performance at Estadio Ramón Sánchez-Pizjuán.

Also in Group G, Marco Reus took his tally to 22 goals in 57 Champions League matches by opening the scoring in Borussia Dortmund's 3-0 win over Copenhagen. U.S. international Gio Reyna set up the other two goals for Dortmund, exchanging passes with English teenager Jude Bellingham in a slick move for the third.

HAZARD STEPS UP

If Benzema has to miss significant time for Madrid, Hazard signaled that he may be ready to pick up some of the slack.

The Belgium playmaker — who was on the bench before replacing Benzema — set up the first two goals before scoring the third himself against Celtic. It was his first Champions League goal in 651 days and first in any competition since January.

Callum McGregor had nearly put Celtic ahead in the first half when he struck a fierce shot against the post in the 21st minute.

In the other Group F game, Maryan Shved scored twice as Ukrainian club Shakhtar Donetsk beat RB Leipzig 4-1. Shakhtar's domestic season only recently started after a lengthy break because of Russia's invasion but the team got some help from Leipzig goalkeeper Peter Gulacsi for the first goal.

Gulacsi made the blunder of the evening by giving the ball away to Shved as he stood well outside his own area, giving the midfielder a simple finish into an empty net.

Leipzig leveled with a goal by French defender Mohamed Simakan in the 57th but Shved restored the lead one minute later.