ROME — Liverpool first tried to sign Piotr Zieliński at the age of 12. Jürgen Klopp made another attempt to acquire the Poland midfielder in 2016 after Robert Lewandowski, who played under Klopp at Borussia Dortmund, had spoken highly of his national team companion.

Liverpool and Klopp got an up close look at what they missed out on when Zieliński scored two goals and assisted on another as Napoli overwhelmed last season’s Champions League finalists 4-1 in the opening round of this campaign’s group stage.

Zieliński’s breakout performance also highlighted what he could contribute for Poland at this year’s World Cup. Cameroon midfielder André-Frank Zambo Anguissa and South Korea center back Kim Min-jae gave hints at their potential for the tournament in Qatar, too, as did possible Argentina reserve Giovanni Simeone.

Khvicha Kvaratskhelia, the 21-year-old Georgia winger who has been tearing up Serie A with four goals in five matches, also showed his ability on the international stage.

And as a whole, Napoli, which leads Serie A in goals, shots and assists, extended its domestic form to Europe in convincing fashion.

“The most important thing is that the squad dominated,” Zieliński said after Wednesday’s match at the Stadio Diego Armando Maradona. “It was a perfect game and we beat a top-level opponent. We’re pleased but we also realize that this is just the start of group play and there are still more tough matches to play.”

Formerly used as a super sub under Maurizio Sarri, the coach who he followed from Empoli to Napoli, Zieliński showed off his full arsenal against Liverpool. First, he earned and converted a penalty. Then he turned provider for Zambo Anguissa, who finished off a give-and-take with the Pole to make it 2-0, before adding another on a rebound of his own shot.

With a high-powered attack featuring Lewandowski, Arkadiusz Milik and Krzysztof Piątek, Zieliński should have plenty of chances to set up more goals in Qatar. Poland is in a group with favorite Argentina and is expected to battle with Mexico for a spot in the next round — with Saudi Arabia rounding out the group.

Likewise, Zambo Anguissa displayed what he could do for Cameroon, which is in a group with Brazil — another tournament favorite — plus Serbia and Switzerland.

Zambo Anguissa dominated against James Milner and 19-year-old Harvey Elliott, perhaps creating some regret among Premier League fans — because Zamba Anguissa was twice loaned abroad by Fulham before signing a permanent contract with Napoli in May.

Speaking of Cameroon, the performance of goalkeeper André Onana was one of the few highlights for Inter Milan in a 2-0 loss to Bayern Munich.

Kim, who Napoli signed to replace defensive stalwart Kalidou Koulibaly, has provided an immediate physical presence in the Partenopei’s back line. Nicknamed “the Monster,” Kim has already scored twice in Serie A.

Another Napoli player with a story to tell is Simeone — the son of Atlético Madrid coach Diego Simeone.

The younger Simeone scored three minutes after he came on for his competition debut and then kissed a tattoo of the Champions League logo that he got on his left wrist at the age of 13. Simeone then provided the cross that led to Zieliński’s second goal.

“I always dreamed of playing in this competition,” he said.

Dad also scored in his Champions League debut 25 years earlier with Atlético — actually with a two-goal performance.

“We showed,” Napoli coach Luciano Spalletti said, “that nothing is impossible.”

Up next for Napoli: a home game against Spezia on Saturday before a visit to Rangers three days later in the next round of the condensed group stage of the Champions League.