Federer rallies to reach Swiss quarterfinals

Roger Federer made it 17 wins in a row at the Swiss Indoors when he defeated Jan-Lennard Struff of Germany 6-3, 7-5 on Thursday to march into the quarterfinals.

The top-seeded Swiss, who was born in Basel, had his serve broken in the third game, but he fought back well by winning five consecutive games to stay on course to reach the final for the 14th time.

The 37-year-old Federer next meets Gilles Simon of France, who knocked out Ernests Gulbis of Latvia 7-6 (4), 7-6 (0).

"I was ready for Struff to come out and swing," Federer said. "I didn't know how aggressive he was going to play, or how much serve and volley he was going to do. But, unfortunately, I didn't have the best first two service games.

"He connected well, he came out with a plan and it worked for him. In the second set it was close throughout, but I think I was able to clean up my game a little bit. I'm happy I improved after a rocky, slow start today, to play well after that. I think the crowd was really into it. They were excited I came back from being a break down."

Second-seeded Alexander Zverev also went through to the last eight with a 6-4, 6-4 victory over Alexei Popyrin, but thirdseeded Marin Cilic was beaten 7-5, 7-6 (2) by Marius Copil.

There were also wins for Stefanos Tsitsipas, Daniil Medvedev, Roberto Bautista Agut and Taylor Fritz.

Pliskova reaches WTA Finals semifinals with win over Kvitova

Karolina Pliskova won the first set to eliminate Petra Kvitova, and then won the second set to advance to the semifinals at the WTA Finals.

Pliskova, who advanced from her group for the second straight year, beat Kvitova 6-3, 6-4 on Thursday to improve her record to 2-1 at the season-ending tournament. It was Pliskova's first victory over Kvitova in their fourth meeting.

"I knew I lost my other matches to her. I knew this time I had a chance because I was playing pretty well in my other two matches here," Pliskova said on court after the match. "Everything is working well for me this week so I'm just happy."

In the other group match, Elina Svitolina stayed unbeaten and advanced to the semifinals by beating defending champion Caroline Wozniacki 5-7, 7-5, 6-3.

Kvitova jumped out to a 3-0 lead in the second set, but Pliskova then won six of the next seven games. Kvitova finished the group with three straight losses.

"I still had a lot of positive thoughts in the match to fight and turn it around, even (if it) didn't happen," Kvitova said. "I still need to be fine because I still have the Fed Cup final (against the United States) coming up."

Kvitova, who is from the Czech Republic, rarely loses to players from her country. Since the 2012 Madrid tournament, the two-time Wimbledon champion has won 27 of 29 matches against Czech opponents.

Her only other loss to a Czech player in that time period was to Pliskova's twin sister, Kristyna, at this year's tournament in Charleston, South Carolina.

Svitolina only needed to win one set in the late match to advance, but she had to wait for it.

Wozniacki nearly pulled off the straight-set victory, which would have given her a place in the semifinals instead. But she squandered two game points in the final game of the second set and then sent a backhand long on a fifth-set point for Svitolina.

"It was an amazing match and a tough fight because Caroline always brings the best out of you," Svitolina said on court. "You have to push your limits against her."

Wozniacki, who finished with a 1-2 record, felt she was second best on the day.

Svitolina believes reaching the semifinals should quiet recent social media comments suggesting she'd lost too much weight.

"It was not easy with all the things going on social media and opinions with my physique," Svitolina said. "This really shows that I'm getting mentally tough and that's what I've been working on really hard. "I've learned there's thousands of opinions, millions of opinions and I need to just do my job."

Former No. 1 Wozniacki has rheumatoid arthritis

Caroline Wozniacki was diagnosed with rheumatoid arthritis before the U.S. Open, the Danish tennis player revealed at the WTA Finals on Thursday.

She made the announcement after being eliminated from the year-end competition following a 5-7, 7-5, 6-3 loss to Elina Svitolina in her third round-robin match.

"It turns out that I have an autoimmune disease, rheumatoid arthritis, which goes in and attacks your joints," she said.

"When the body has a lot of fluids in it and you swell up, you get tired, you get exhausted, all these things.

"In the beginning, it was a shock. You feel like you're the fittest athlete out there. That's what I'm known for, and all of a sudden you have this to work with."

The 28-year-old Wozniacki won her first Grand Slam title at the 2018 Australian Open. She briefly recaptured the No. 1 ranking after a six-year wait.

After Wimbledon in July, she thought she had the flu while on vacation. Her legs hurt when she started playing again. In August in Montreal, she woke up one morning and couldn't lift her arms above her head.

Wozniacki thought she may have glandular fever, but the doctor said she was fine. However, she was certain something was wrong and went for more in-depth testing.

She won her third title of the year in Beijing three weeks ago. She said it was initially important to keep the diagnosis a secret.

"I didn't want to talk about it, obviously, during the year because I didn't want to give anyone the edge or thinking that I'm not feeling well," she said. "You learn how to just cope after matches.

"Some days you wake up and you can't get out of bed, and you just have to know that's how it is, but other days you're fine. You don't even feel like you have it. I didn't want to look it up, I didn't want to Google it, because if you Google stuff you feel like you're going to die," Wozniacki added with a smile.

After the U.S. Open in September, she decided to do more research on rheumatoid arthritis and her doctor said much progress had been made in managing the disease.

"You just have to be positive and work with it, and there are ways you can feel better, so that's great," Wozniacki said. "It's, obviously, not ideal for anybody. I think when you're a professional athlete, it's even more not ideal.

"But at the end of the day, you find a plan, figure out what to do, do your research, and thankfully there are great things now that you can do about it. I'm very proud of how I have been so positive through it all and just kind of tried to not let that hinder me."