INDIAN WELLS, CA, USA - Down but never out, Venus Williams scored a big win from a big deficit at the BNP Paribas Open on Saturday.

The seven-time major champion rallied from a set and a double break down to stun No.3 seed and Australian Open runner-up Petra Kvitova, 4-6, 7-5, 6-4.

Trailing 6-4, 3-0 in the match, Williams forced what might be the most improbable final set of the pair's head-to-head to date, as the two Grand Slam champions have now played three sets in all seven of their career meetings. 

"A double break is not ideal against a great server, especially a left-handed server. But the good part is being in matches, you just -- a lot of it is just being in the moment," Williams said after the match.

"I think I created some opportunities. I had some good points. I think she had a few tight points, and here we are.

"It seemed like I played even better when I was down. I really didn't have any other choice because she was playing so well and serving so well. So it's nice to know that in that sort of situation I can still play and just lift my level."

After winning seven of the last nine games of the second set to draw level, the seven-time major champion faced another deficit in the third set, and won the last three games, again from a break down, of the match to seal a spot in the third round opposite compatriot Christina McHale. 

Despite an off day from one of her biggest weapons - the American didn't hit an ace over the course of nearly two-and-a-half hours, and lost serve four times - it was her consistency in protracted rallies which helped her pull off the comeback.

"The match we played was definitely worthy of a final. It's not ideal for her to see me in her part of the draw. I don't think anybody wants that. So I'm sure for her it was just not ideal," Williams said.

"Definitely being down in those last two sets, it's definitely not easy to turn it around. That's for sure. I like to also know that I have opportunities all the time and that I can create those. So even when it's not looking great, I know that the match isn't over yet."

Kvitova racked up 10 aces, but also 10 double faults, and despite more than doubling Williams' total of winners (38 to 15), she also more than doubled her total of unforced errors (56 to 25).

"It was such a weird match, to be honest. We started, I think, pretty nervous, both. I took the first set. Suddenly I was leading in the second, but somehow I just gave her a chance again to be back in the match, and she took it," Kvitova said in defeat.

"Suddenly, she just started to play better, I started to play worse, and that's why that happen to the third set, which I didn't break up, but I don't know. I was so frustrated with myself from the half of the second set to the end, which shouldn't happen to me.

"It's always tough to play Venus, for sure. We always play three-setters, and suddenly, we have been there again and playing until the end, and in the end of the match, she definitely played better than me."