Leicester's fairytale Premier League title success was built on a miserly defence, but they have suffered some heavy losses already this season, most recently losing 4-1 at Manchester United.
They produced a far more dogged display against Porto on Tuesday, with Islam Slimani's 25th-minute header and a spirited rearguard action helping to procure a second successive group G win.
"I'm happy when I see my players play like tonight, with our spirit," said Ranieri, whose side were playing their first home game in the Champions League in the club's 132-year history.
"I recognise this team when it plays together as a team. If we play in this way, I'm not surprised.
"I was surprised when we conceded three goals on a corner on Saturday (at United). Very, very surprised.
"I spoke a lot about corners, to maintain the clean sheet. My players were very, very concentrated; strong, attentive in every situation. It was good for everybody after the bad defeat in Manchester.
"We showed very good character, attitude and personality. Particularly in the last 10 minutes when Porto tried to equalise. We were very calm, very attentive and closed all the spaces."
Leicester's win left them two points clear of FC Copenhagen at the group G summit ahead of the two sides' meeting at the King Power on 18 October.
But, ever cautious, Ranieri said it was far too early to start thinking about the last 16.
"I'm waiting. I'm San Tommaso (Saint Thomas): if I touch, I believe," said the Italian.
"Now we have to continue to stay calm. Copenhagen won 4-0 (against Club Brugge), are very well organised, drew 1-1 in Porto.
"It is very important for us now to clean our minds and go back in the Premier League.
This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.
ConversionConversion EmoticonEmoticon