The first Top 10 upset at this year's French Open belongs to Slovenia's Tamara Zidansek.

In a staggering three hours and 20 minutes, the world No.85 ousted No.6 seed Bianca Andreescu, 6-7(1), 7-6(6), 9-7, in the first women's match to extend past 6-6 in the deciding set at the event. 

Having stretched a seeded player to three sets in the first round of the French Open in each of the past two years - Elise Mertens in 2019 and Garbiñe Muguruza in 2020 - Zidansek finally scored her first-ever main-draw win in Paris, and first Top 10 win, with a thrilling comeback, as she not only rallied from a set behind, but from a break down in the decider.

Zidansek had previously been 0-4 against Top 10 players in her career, but did stretch world No.1 Ashleigh Barty to a decider in the second round of the Mutua Madrid Open earlier this spring.

"Obviously, the first Top 10 win is a big one. It shows me that I can play with players like that, and I showed today that I can beat them," Zidansek said after the match. 

"Clay courts are my favorite surface for now, and this is a pretty big tournament for me. I've been trying to improve my game tactically, mentally, just the whole package. It's a big win for me today.

"I just kept fighting, I kept telling myself that it can turn either way, because last year, I had a similar match in the first round. I did have that experience, and I know how it feels to be in a match like that, so I think that experience helped me today."

A two-time champion at the WTA 125K event in Bol, Croatia, and runner-up at the Copa Colsanitas in Bogota earlier this year, Zidansek matched the 2019 US Open champion shot-fo-shot on her preferred surface, hitting one more winner than Andreescu (41 to 40) and 16 less errors (46 to 62). 

Nonetheless, Andreescu was two points away from victory deep in the third, buoyed by vocal support from the French crowd: following eight holds of serve, the Canadian was the first to break at 4-4 to serve for the win. In that crucial game, Andreescu held a 30-15 lead, but three miscues off her forehand - including one just millimeters wide which would've otherwise given her two match points - gave Zidansek second life. 

She later saved two break points serving at 7-7, and won seven of the last eight points in the match.

"I didn't start really well, but the conditions out there are tough. It's windy so you have to get used to it. I just kept getting into the match more and more," the Slovenian continued.

"I think my serve was a great example of that. I didn't start well, but in the second set, I was serving better. In the third set, I was serving really well, which helped me save those break points at 7-7. I was serving really well when I was break point down, and I remember she hit a great return crosscourt, very deep, and I managed to get it back."

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The match's dramatic conclusion was foreshadowed as early as its early games, as a straightforward beginning for the No.6 seed quickly became complicated: after winning 12 of the first 18 points to build a 3-0, double-break lead, Andreescu lost four straight and found herself staring at a 0-40 deficit on serve to lose a fifth. 

Andreescu nonetheless held serve in that game - one of two service holds that she secured from 0-40 in the match - and eventually moved a set ahead thanks to a near-perfect tiebreak, though she saved a set point on serve in the 10th game before doing so. 

"From my part, I didn't feel like I played good tennis today. But at the same time, she played really, really well. She threw me off a lot with her heavy, spinny shots and her variety," Andreescu said in defeat.

"But at least thinking on the positive side, I'm healthy, and I was able to fight as hard as I could. Physically I felt good. I started to get a little bit tired at one point, but I think it mainly came from the mental side of things, because today I didn't feel like I could control my emotions as well as I normally do.

"I tried my best with what I had today, but Tamara just really, really played well. And, yeah, that's all I can say really. I just have to learn for the next one."

Undaunted by the deficit, Zidansek used a heavy, topspin forehand to dictate her fair share of rallies, and led by a break three times in the middle set before ultimately forcing a decider. Unable to serve it out at 6-5, Zidansek made no mistake in the tiebreak, and won both the first three, and last three points in the breaker to set up the thrilling finale. 

"Each player has a different path. Some players, they go out there and they win big matches when they're 16 and 17, but I'm 23 now and for me, it's been a process. I work hard and I was never top-ranked in under-14, under-16, so I was like the underdog, I guess. I've just been trying to make my way up there, and I guess that made me strong. It developed my personality as well, so I think it's all coming together right now."

- Tamara Zidansek

Zidansek advances to a second-round meeting against American Madison Brengle, who ended the run of Colombian qualifier Maria Camila Osorio Serrano, the Bogota champion, in straights, 7-5, 6-4. 

Later in the day, Sofia Kenin avoided being the second Top 10 seed to fall. In a hotly-anticipated opening match, the No.4 seed and 2020 runner-up overcame 2017 French Open champion Jelena Ostapenko in three sets, 6-4, 4-6, 6-3. The American arrived in Paris winless on clay this spring, having lost to Lauren Davis, Anett Kontaveit and Barbora Krejcikova in Charleston, Stuttgart and Rome. 

In the aftermath of her Australian Open win last year, Kenin lost to Ostapenko in a competitive three-setter in the Billie Jean King Cup, but leveled the head-to-head between the two major-winners in a match that lasted just over two hours on Court Suzanne-Lenglen.

"I'm really happy with the way I played. I fought out there. She's such a tough player to play. I know her game quite well since I practiced with her during quarantine in Australia. I kind of knew what to expect from her," Kenin said.

"She's a tough player, a great player. I had to really play some really good tennis and really fight out there if I wanted to win."

Though the first two sets were identical on the scoreboard, they couldn't have unfolded more differently. Kenin rallied from 2-0 and 3-1 down in the opener to ultimately win it, but couldn't do the same in the second after leveling from 4-1 behind. 

The final set was dominated by the returner, with Kenin and Ostapenko combining to break each other's serve eight times. Kenin's hold to 15 to lead 2-0 was ultimately the decisive game, while she bookended the set with breaks to love. 

After facing another Grand Slam champion, Kenin will next face another American in qualifier Hailey Baptiste. The 19-year-old from Washington, D.C., ranked World No.202, scored her first Grand Slam in a main draw over Anna Blinkova, 6-1, 6-4. 

"I have no idea how she plays. I've never watched her. It will be an interesting match," Kenin added. 

"I'm taking it one match at a time. I'm not looking into what's going to happen later. For me it was baby steps to get through round one, since obviously it's never easy getting through to the first round during a Grand Slam."

Elsewhere for seeded players and crowd favorites, No.14 Mertens rallied from 1-4 down in the first set to beat Aussie qualifier Storm Sanders, 6-4, 6-1, while France's Caroline Garcia eased to a 6-3, 6-1 win over Laura Siegemund, a quarterfinalist at last year's tournament.