The most anticipated opening-round match of the Wimbledon women's draw delivered the fortnight's first major upset.

In the lone first-round match between two former Grand Slam champions in the draw, 2017 US Open winner Sloane Stephens was comprehensive from start to finish to defeat No.10 seed and two-time Wimbledon winner Petra Kvitova on Centre Court 6-3, 6-4.

Stephens was forced out of the only grass-court event she entered last week in Bad Homburg with a foot injury but showed no signs of rust or injury over the course of 77 minutes, improving her head-to-head record against Kvitova to 3-1.

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"I haven't played on grass in two years. This is my first match back. I think for me it was more of just executing my game. I knew I needed to serve well and return well," Stephens said after the match.

"Obviously a lefty on grass is like your worst nightmare. I was super prepared to be diving for balls on the return, but I knew that I had to fight for every ball and make sure that I got my racquet on a lot of those balls.

"I did that super well today. Instead of being super passive, I was super aggressive on the returns. I was trying to make her play and be on her back foot. Obviously she likes to play super aggressive and inside the court. I knew I needed to play first-ball tennis, and I did that pretty well today, which is good.

"It's a great build, a great first match. Obviously, grass or not, wanting to get a good win like this is really important. I think not only for this tournament but going into the rest of the season, for me, it's pretty big. I'm excited to have a good win here and hopefully continue to play some good tennis."

Broken in the first game of the match, Stephens never again lost serve and broke the Czech left-hander three times.

She later denied Kvitova an opportunity to climb back into the match in the second set by saving four break points in a crucial hold for 3-3 and broke serve in Kvitova's ensuing service game to take a lead she'd never relinquish. 

"I'm very disappointed. I'm sad I lost in my first round here. I'm glad I can be here after two years missing it. And I know also that there are much tougher, harder times in the life than just losing the match. Of course, it hurts. On the other hand, I know there are more important things in life."

- Petra Kvitova

In all, Kvitova could not find a way to hit through Stephens' expert counterpunching. The left-hander racked up 20 unforced errors to just eight winners in the match, while Stephens totaled 12 winners and 14 unforced. Stephens also landed 78 percent of her first serves and collected a trio of aces. 

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"It was tough first round, for sure. I felt that I do have a kind of ability to win the match. I just didn't find the best for me today. It was really tough. I just didn't play the best. I think that she played really solid. She was just better today," Kvitova said.

"I have to say that she served very well. I didn't really know that she's playing that well on the grass, to be honest. ... She really surprised me kind of. She didn't miss at all, I would say. She was moving very well.

"It was tough for me to get to the final shots as well. My game, which I love to open the court a little bit more. But I just couldn't make it. I just felt like little bit under pressure as well. She played pretty long balls as well, very deep. It was a bit difficult for me to find something. With the nerves, and not really great movement from my side, it was just a bit difficult."

Up next for Stephens, now ranked world No.73, is her American compatriot, lucky loser Kristie Ahn, who overcame Great Britain's Heather Watson in a late-night thriller 2-6, 7-6(3), 8-6.

Moved to No.1 Court as the fourth match due to the day's rain, Ahn rallied from a break down twice in the third set, saving a match point, to seal the 3-hour, 3-minute victory which ended at 10:17 p.m. local time.