It was Lewandowski's third goal in two games following his double that gave Barca a 2-1 fightback win at Valencia last weekend.
"I know Robert (Lewandowski) really well and I don't think he has returned to form because that's how I have always seen him as a player," Flick told DAZN.
Under Flick's management at Bayern Munich in the 2019-20 and 2020-21 seasons, Lewandowski scored 83 goals in 71 matches, winning several major titles including the 2020 Champions League.
"I'm happy with him because it's not only the goals he scores, it's his collective effort, the way he dedicates himself to pressing high and very effectively," Flick said.
"Physically, he is 100%. He is a total professional, who takes fitness very seriously. He knows how to handle pressure and we saw that after the equaliser in the second half. He is a great player."
Flick also commended Brazilian winger Raphinha, who excelled again playing as an attacking midfielder.
"Rafa can play in any attacking position. He can play as a 10 or he can change positions, he is phenomenal in pressing. We needed someone like him as we are still missing some players," Flick said.
Gavi, Ronald Araujo and Frenkie De Jong are all out with injuries and new signing Dani Olmo has yet to be registered with LaLiga due to Barca's breach of Financial Fair Play (FFP) rules.
"I must be very happy after two wins against such tough opponents and under the circumstances," Flick said.
"We have injuries and players who can't play but what we can't control we don't have to ignore. Defensively we are doing well."
