Lewandowski, 34, took his tally for Barca to eight in five games since his €45 million move from Bayern Munich, while he also moved past Karim Benzema to become the third highest scorer in the history of the Champions League.
“I am running out of praise for him,” Xavi said after the game. “He’s scored a hat trick, but it’s not just that. It’s how he plays and how he makes the team play, finding the third man, reading the space perfectly, pressing…
“I am delighted [with him]. He has been a fantastic signing. He gives us so many solutions in attack, he’s a leader, a winner… [just] a fantastic, fantastic signing.”
Franck Kessie had opened the scoring for Barca before Lewandowski struck his treble, becoming the first player to score Champions League hat tricks for three different teams, having done so previously for Borussia Dortmund and Bayern Munich.
“I don’t know if he is the best No.9 in the world, but he is the best No. 9 for us,” Xavi added when asked if there is a better striker in the game than the in-form Lewandowski.
“If he is not the best, he is up there with Benzema and the others, [Erling] Haaland is also there. But, without making comparisons, Robert is spectacular and it is an honour to have him on the team.”
Substitute Ferran Torres added Barca’s fifth goal at Camp Nou, latching on to a pass from Ousmane Dembele. The French winger had earlier set up Lewandowski’s second goal, too, and Xavi sees elements of Paris Saint-Germain forward Neymar in him.
“There are not many in football like him, in terms of a pure winger who is very difficult to defend against,” the Barca boss said.
“We have to take advantage of his qualities. He is happy, he’s enjoying himself. He’s an important player who makes the difference, scoring goals, creating… he’s a dagger on the wing.
“The quality he has one-on-one is at the level of Neymar when he’s at his best. He must be more daring and shoot more, but he is a good kid and he’s making the difference in games.”
Barca remain unbeaten across five games in all competitions this season, but Xavi says it’s too early to say they are back after winning just one Copa del Rey in the last three seasons.
Bigger tests remain, especially in Europe. The Blaugrana visit Bayern Munich on Tuesday in the Champions League after the German champions began their campaign with a 2-0 win away at Inter Milan on Wednesday in the group’s other game.
“It’s soon to say [Barca are back],” Xavi added. “We are very happy with the performance, but it is just three points and one game at home. We still have to go to Munich, to Milan. It’s a difficult group. We must remain humble; this is just getting started.”