The Czech Republic defender was handed his bow against Liverpool on Sunday, with boss Jose Mourinho turning to the 20-year-old centre-back for a crunch clash at Anfield.
Kalas acquitted himself well, helping to keep a clean sheet as Chelsea blew the title race wide open with a 2-0 win.
He is delighted to have come through such a tough first test and believes he settled quickly alongside Branislav Ivanovic.
Asked he felt apprehensive about being thrown in at the deep end, Kalas told sport-invest.cz: "No, and I must admit that surprised me.
"Maybe it was like that because I only learned about my presence in the starting XI on Sunday, so I didn't have time to get nervous.
"The manager asked, jokingly, the most experienced players who they had made their debuts against in the Premier League. They were recalling various clubs and Mourinho told me, 'See, you will have Liverpool for your debut'.
"I believe that we then put the theory of centre-backs needing a lot of time to get used to one another upside down.
"Hopefully people couldn't tell that it was my first game. Naturally, I learned where I need to improve and I what I have to work on, but overall I had a good feeling."
Next up for Chelsea, who are now just two points off the pace in the race for the Premier League crown, is a meeting with Atletico Madrid.
Their UEFA Champions League semi-final is locked at 0-0 following a Spanish stalemate in the first leg, and Brazilian playmaker Willian admits it is now up to Mourinho's men to ensure that they complete the job on home soil.
Ahead of what promises to be another epic European encounter at Stamford Bridge, he told Lancenet: "The team is now completely focused on Wednesday's game, which is very important.
"We have the chance to reach the Champions League final, which is every player's dream.
"We are optimistic. We are playing at home, where our team always does well.
"We have to mark them tightly and take advantage of the chances we get. We are confident and will try to advance."