Kvitova had made a quicker than expected recovery from the career-threatening injury sustained to her left, playing hand to compete at Roland Garros. "I think I played well after six months off", said Kvitova, adding that she regarded herself as a victor already.
Then, addressing her guest box, which included her parents and brother, she said: "Thank you for everything you helped me through (in) this hard time".
Kvitova, 26, was injured when an intruder, under the pretense of checking a utility meter, entered her apartment in Prostejov.
But Muguruza might just be playing herself into form again at just the right time following a year of struggle and powered her way to a 6-7 (4/7) 6-4 6-2 victory in two hours and seven minutes. "I'm not here to sit and talk with you guys, but - that's nice, as well", a smiling Kvitova told reporters.
"I promised my doctor, who gave me the green light, that if I feel pain in my hand during the match or in the practice, I'm stopping immediately". "I am shaken, but fortunate to be alive".
Kerber can lose her No1 ranking by the end of Roland Garros if Simona Halep wins the title in Paris or Karolina Pliskova reaches the final.
PARIS (AP) - Sweat-soaked and still wearing her match outfit, Petra Kvitova was looking for someone to hug as she wandered into the players' lounge in the French Open's main stadium shortly after leaving the court Sunday. But I really fought. Two-time Wimbledon champion Kvitova downed outclassed Julia Boserup of the United States 6-3, 6-2, falling to her knees in celebration in the moment of victory before weeping at the net.
Kvitova had not played in a tournament since she was stabbed during an attack at her home in the Czech Republic in December.
"Well", she said, "that's unbelievable". "But, yeah, now I can not changing anymore and trying to looking forward".
"I was also fighting with my emotions not to wait for a mistake (by Kerber)", she said courtside. Mattek-Sands looks for her first third round appearance in a grand slam since the 2015 US Open.
"Of course I'm disappointed that the clay court season was not so good".
"Yesterday I was thinking how everything will be, and I couldn't really imagine how that's going to be".
On Sunday, Kerber fell a double break down to trail 5-1 to her 28-year-old Russian opponent who she was facing for the 12th time.
Kvitova had initially targeted Wimbledon, where she won the title twice in 2011 and 2014, for her comeback but she progressed faster and, therefore, chose to head to Paris. Her backhand was shaky at times and she did not move forward well in the court, but the foundations were more than solid.