ROME -- No.6 Elena Rybakina advanced to the semifinals of the Internazionali BNL d'Italia after two-time defending champion Iga Swiatek was forced to retire with a right thigh injury. The reigning Wimbledon champion advanced to her first WTA 1000 semifinal on clay after Swiatek retired at 2-6, 7-6(3), 2-2.

Rybakina will face No.20 Jelena Ostapenko in the semifinals on Friday. 

Ostapenko beats Badosa to make first clay semifinal since winning Roland Garros

With wins over Swiatek at the Australian Open and Indian Wells earlier this year, Rybakina is now 3-2 against reigning World No.1s in her career. The 23-year-old is into her third WTA 1000 semifinal of the season.

Swiatek's retirement ends her 14-match win streak at the Foro Italico. She had won the titles the past two years. 

Story of the match: In the fourth installment of the rivalry between the reigning Roland Garros champion and Wimbledon champion, Swiatek's clay-court prowess was on full display early as she looked to level their head-to-head record to 2-2. Rybakina had yet to drop a set in Rome and was bidding to advance to her third WTA 1000 semifinal of the season and first of her career on clay. 

Facing the player who accounted for two of her five losses this season, Swiatek was the picture of focus and intensity from the first game. Not even a humorous interruption in the first game could put the two-time French Open champion off. With a flurry of return winners, Swiatek broke Rybakina in her opening service game and repeated the feat two games later to open a double-break lead at 3-0.

Rybakina would finally get on the board at 4-1, but the Indian Wells champion struggled to do damage with her serve and forehand. Swiatek deftly absorbed Rybakina's pace and drew errors, while out-striking her opponent as well. Behind 11 winners to just five unforced errors, Swiatek sealed a dominant opening set in 44 minutes.

Swiatek carried her momentum into the early stages of the second set. She broke Rybakina immediately and would build a 3-1 lead.

"It was a really tough match, especially the beginning," Rybakina said. "I would say I didn't start that good. With Iga she was really aggressive from the beginning, she was more explosive, she was moving better. I was struggling with the first serve in the first set a lot, so it was not really helping me to play every time with a second serve. In the second set, I started to feel a little bit better."

Turning point: Rybakina would have to wait until 6-2, 4-3 before she saw her first break point chance of the match. Down 15-30, Swiatek fired a forehand wide to give Rybakina two chances to get back on serve. She needed just one, as Swiatek landed another driven forehand wide to even the set at 4-4. Rybakina carried that resilience into her next service game, where she wiped out three break points from 15-40 down and hold to 5-4.

In the tiebreak, Rybakina showed why she has lost just one tiebreak this season. The Kazakh played it perfectly to move that record to 9-1 and take the match into a third set after two hours of play.

Injury concern for Swiatek: On the penultimate point of the second-set tiebreak, Swiatek came out of a slide wincing. She took a medical timeout during the set break and returned with strapping around her upper right leg. 

When play resumed, Swiatek gamely tested her movement for four games. After Rybakina held serve to 2-2, Swiatek walked to the net to shake hands, ending the 2-hour and 20-minute duel.

"I saw something happen in the tiebreak, on almost the last point but I didn't know how serious it is," Rybakina said. "I saw that the first two games she started really aggressive so I understood that she couldn't really move that much. but she was still making good returns and I knew that I had to be focused. I know myself that if anything is hurting you're trying to go for it and a lot of times it works. So she probably did the same, but after, I guess it was too much."

Words from the winner: "I was coming to this match without any expectations and I'm just happy that in the second set I started to feel much better the forehand and started to move better," Rybakina said. "So I think it was just good from me overall no matter the result. Just happy to play another match and looking forward to it."