The No.2-seeded Kvitova looked to be in cruise control in the first half of the match, storming out to a 6-3, 3-1 lead, and even holding two points for 6-3, 4-1, but the match turned on a dime from there as the No.28-seeded Jankovic began hitting all the right targets, and she dug it out, 3-6, 7-5, 6-4.
"I'm overwhelmed. I'm so excited. My heart is still pumping," Jankovic said afterwards.
"Playing on grass is very difficult for me - it doesn't come naturally. But playing on Centre Court against the defending champion was just unbelievable. I'm really really happy to win this match!"
How did she claw out of being a set and a break down?
"It didn't matter how badly I was playing or what was happening out there, I really just tried to stay one point at a time and fight, and when I won that second set I knew I just had to keep going out there.
"When I won, I couldn't believe what just happened. I lost to Petra the last time we played in Rome, and I know she plays amazing here. But that's what this sport is all about. It's such a great excitement for me - I'm so glad I was able to win and this gives me a lot of confidence the rest of the tournament."
The former World No.1's win over the World No.2 was her biggest ever win at a Grand Slam.
Kvitova was asked about the defeat in her post-match press conference.
"It's tough to explain," the Czech said. "I'm not really sure what happened out there. I was kind of up in the second set, and then suddenly I felt like she was coming back and playing a little bit more aggressive. Suddenly from my side I didn't have an answer for it - my serve didn't help me, either.
"I was really struggling with each shot that I played from there."
Her disappointment was evident as she was asked what it feels like to be a two-time champion here.
"To be champion of Wimbledon is something really special. That's why I'm playing tennis, and that's why I feel lucky to win it here," Kvitova said. "It's not great to lose in the third round. Not to be in the second week of my favorite tournament is really sad. I don't really know what else I can say - that's it."