PARIS, France - Unseeded Czech Katerina Siniakova scored herself a statement victory in the first round of the French Open on Monday, defeating former World No.1 and two-time Australian Open champion Victoria Azarenka, 7-5, 7-5.

It was a tale of two contrasting sets for the duration of the one hour, 47 minute encounter, as neither player dropped serve - or even faced a break point - until the final game of the first set when Siniakova edged in front.

In the second set, the World No.57 trailed by a break three times, but ultimately won four of the last five games of the match to score her first-ever main draw victory at Roland Garros. 

"I had some good practice days finally after Rome, but it didn't come out on the court today," Azarenka told reporters in defeat. "Obviously, losing a first round is very disappointing. Even though I'm doing good things in practice, I am not able to transfer it to the match.

"I really need to kind of take a look of what I can do better. This French Open is done and it's very disappointing, but I can have some time to prepare now and take another two weeks to do a little bit of more, like, preseason training which I really, really need."

The Czech struck 25 winners to 23 unforced errors over the course of the match, with her controlled aggression outweighing Azarenka's 27 winners to 38 unforced errors.

"It's hard for me to expect to play steady right now with one level. I haven't played in a while, and I haven't been able to prepare that I want to prepare," Azarenka assessed after the match.

"I know there is going to be up and downs in my game, and I have to work through them. I did work through them. I just didn't find the right choices today, and I have to just keep going.

"It's not going to be easy way for me. I need to get back and to practice, and I need to figure some things out why I'm not doing the right things that I do in the practice during the matches. I need to figure out how to make that transition."

A pair of victories over Grand Slam champions will ensure that Siniakova and Kateryna Kozlova will clash for their first-ever appearance in the third round of the French Open, after the Ukrainian upset defending champion Jelena Ostapenko on Sunday.