Petra Kvitova had to work hard to defeat Kozlova in the 2nd round of the US Open and it included a saved set point. After she did though, it was all smooth sailing for her and she ended the match with 7-6(3) 6-2. Speaking about the match and 1st set in particular she said:

"In the first set, it was kind of tough. I was really fighting a little bit the opponent, but with myself as well. There was a lot of nerves over there. I lost my serve and I was still down, and I still tried to come back and answer."

The crucial part of the game was the tiebreak in which Kvitova played better and deservedly won. Her confidence got a boost after the set victory and it showed on the court. About that, Kvitova said:

"When I won the tiebreak in the first set, it's been a little bit easier. I was more relaxed, more, kind of, calmer. That really helped me. Beginning of the second set I got the break, and it was a little bit easier for me to -- I was breathing a little bit more free."

https://twitter.com/usopen/status/1301264315039846400