Rising Argentine star Nadia Podoroska added another name to a growing list of big career wins on Wednesday in Rome: the legendary Serena Williams.

Using the entire clay-court repertoire that brought her to the French Open semifinals last October, from heavy topspin forehands to adept sliding defense, the World No.44 scored a second-round upset of the 23-time Grand Slam champion and No.8 seed at the Internazionali BNL d'Italia, 7-6(6), 7-5 in one hour and 58 minutes.

The victory over the World No.8 is Podoroska's third career win over a Top 10 player, all in the last eight months.

"It's special win. [To] play against her, it's an honor for me. I saw her playing when I grew up, so it was a special match for me," Podoroska said after the match.

"But most of all, I'm happy the way I played. I felt again comfortable on clay, on my game, and that's most important for me. I think it was a very good match, high level. I knew that I have to play every point, fight for every ball. She didn't play a tournament for a while, so I knew that maybe she did too many mistakes at the beginning or I have to push her to do them. But I think I played a great match."

It also marked just the second time that Podoroska has won consecutive matches this season, having previously come from a set down to beat Germany's Laura Siegemund in her opener. 

"Since Roland Garros, I think for sure it's the best tennis that I play on clay, no? It's also my first tournament [on clay] after that. I played a few weeks ago the Billie Jean [King Cup against Kazakhstan], but I wasn't comfortable playing on clay at that moment. So, yeah, I think it's the best tennis I play."

Podoroska stuns Serena Williams for R16 berth: Rome Highlights

Podoroska twice led by a break in the opener, first at 2-1 and later serving for a one-set lead at 5-4, and was two points away from wrapping up the set much earlier than she did. Later on, the Argentine led 5-1 and 6-3 in the tiebreak, but needed a total of four set points to move in front.

Podoroska doubled her winner-to-unforced error total in the set with 14 in the former and just seven in the latter, as Williams hit 22 winners to just 18 unforced. 

"I'm not playing as many matches. I'm just doing a lot of training. So it's actually really good to get out and to play some matches... My season doesn't usually start this late on clay. But the training isn't for nothing, so I know that it's just a matter of time."

- Serena Williams on her first match since the Australian Open.

In the second set, Podoroska quickly seized command of the match at 7-6(6), 5-2, after navigating a tough hold in a fifth game where she trailed 0-30 at 2-2.

Though she dropped serve at love when she attempted to serve out victory the first time, she stayed steely in the set's late moments and broke once more to secure a statement victory.

"It's tough to have a first match on clay. It was definitely kind of good to go the distance and to try to be out there, but clearly I can do legions better," Williams added. 

"She has a good game, for sure, obviously. She's very consistent. Overall, it was good for me to play such a clay court player on clay today, but it's a little frustrating. But it's all right. It is what it is.

"I have been training for months, but it feels definitely different on clay to make that last adjustment. Just filling out the game, finding the rhythm. Even sliding and confidence with that, with movement... That's always like a little struggle in the first two matches, and then I'm raring to go."

Elsewhere, there were mixed fortunes for other Grand Slam champions.

Most notably, No.3 seed and defending champion Simona Halep was forced to retire with a left calf injury in the second set of her match against fellow former World No.1 Angelique Kerber.

"Unfortunately, an ultrasound has revealed that I have a tear in my left calf. I will get an MRI tomorrow to understand the injury in more detail, but at the moment, we are unsure of recovery time. I’m so disappointed to end my tournament in Rome like this, but I will do everything I can to take care of the injury and be back as soon as possible. Thanks so much for your support and I’ll keep you posted on my progress."

- Post-match statement from Simona Halep on her injury.

Halep was leading, 6-1, 3-3, before getting injured mid-game. 

"In the first set I think my start was a little bit slow. I was not moving too good. I know that I have to move good against Simona, that the rallies are long. I was not serving actually too good in the first few service games on my serve," Kerber said after the match.

"In the second set I knew, 'Okay, now I have to fight for every ball, I have to move better, and maybe not overthink everything.' Also not looking on the scoreboard. Just playing point by point. I was focusing more on my service game, because I start to play better in the second set. Then suddenly she called the trainer. I know that Simona is not calling trainers just like this.

"I knew, 'Okay, something happened.' But I really didn't see the moment, so I don't know what exactly happened in the moment. But, of course, I was feeling so bad with her, because this is not the way I would like to finish a tough match against also a friend on the other side."

"I was trying to helping her as much as I can, but yeah, I hope that she will get very soon back and it's not too bad," Kerber said of their post-match moments.

"I think over the time, I mean, we share the tour together. We know each other very well on and off courts. This is our life on tour now, so we get through all of these situations the last year, especially now.

"We played also doubles in Miami, so it's also a lot of fun we had there. When you're getting older, I think it's also a little bit easier for us [to be friends]. We are very good friends. That's why I'm really also not really feeling great when I see something like this what's happen today. I hope that she recovers soon."

Kerber will next face another former French Open champion, Jelena Ostapenko, for a spot in the quarterfinals. The Latvian took out Aussie qualifier Ajla Tomljanovic in second-round action, 6-2, 7-6(3).

"I think it will be completely different match, but it's also a good match before Roland Garros to have," Kerber said. "I have to play a little bit differently than against Simona, and also like my match against [Alizé] Cornet last night. It's more like that I have to be more aggressive, moving good.

"But of course the plan A is always focusing on me and then how my opponents are playing. But of course I think they are a little bit shorter rallies but faster rallies."

Jimmie48/WTA

No.15 seed and reigning French Open winner Iga Swiatek came through a tough match against former Rome and US Open finalist Madison Keys, 7-5, 6-1. However, after missing Madrid, No.4 seed and 2020 Australian Open champion Sofia Kenin was beaten in straight sets by Barbora Krejcikova, 6-1, 6-4, to drop to 0-3 on clay this season.

From 5-3 down in the opening set, Swiatek reeled off nine games in a row and saved three set points en route to advancing to a third-round meeting with Krejcikova.

"I feel like at the beginning my serve wasn't really working, and Madison was playing really fast," Swiatek said after the match.

"It was tricky, but then I got into the rhythm and it was similar to the first round when I was coming back game after game and just trying to be patient and wait for my game. It came finally."