INDIAN WELLS, Calif. – It was Retro Tuesday at the BNP Paribas Open, as Caroline Wozniacki defeated Angelique Kerber 6-4, 6-2 to advance to the quarterfinals.

Playing for the 16th time, the 30-somethings renewed their compelling rivalry, revealing some of the assorted aches and pains that come with age. It’s now, appropriately, a dead heat at eight wins apiece. This was their first meeting in six years.

And so, it feels like 2011 all over again, when a still-wet-behind-the-ears Wozniacki, at the age of 20, was the winner here in Indian Wells. Barack Obama was the United States president, Rafael Nadal still had eight more Roland Garros titles in him and Coco Gauff was seven years old.

“I could see her struggling with her back,” said Wozniacki, a mother of two, in her on-court interview. “Yeah, I’m just happy I won.

“I don’t take anything for granted. I took a very long break. To be back here in this sport, I’m just enjoying myself. I’m thrilled I get another match.”

Ah, the restorative healing powers of the desert. 

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Kerber, 36, came to California 1-6 for 2024 after a 17-month sabbatical to give birth to a daughter, Liana. She promptly ran off three straight wins before her serve let her down. Wozniacki, 33, was 1-3, but has now put together four consecutive victories and will meet the winner of the later match between No.1 Iga Swiatek and Yulia Putintseva in Thursday’s quarterfinals.

The winner of that match will face either Marta Kostyuk or Anastasia Potapova in Friday's semifinals. Potapova ended Dubai champion Jasmine Paolini's seven-match win streak to make her second WTA 1000 quarterfinal. Kostyuk followed with a straight-set win over Anastasia Pavlyuchenkova to make her first career WTA 1000 final eight. 

For Wozniacki, it was the 156th win at a WTA 1000 hard-court event, equaling another good friend, Agnieszka Radwanska, for the most since the format was introduced 15 years ago. Only Lindsay Davenport (47) and Maria Sharapova (38) have more than Wozniacki’s 36 wins at Indian Wells.

Even from Stadium 2’s swanky seats, it was difficult to tell these two apart -- they could have been tanned twins, wearing matching black-and-white Adidas dresses and visors, mirror images hitting acutely angled shots from the left- and right-hand sides.

Wozniacki was serving for the first set at 5-1, but Kerber rallied and broke back -- twice, in fact -- to wrench it back on serve at 4-5. That was when the Dane called for the trainer and had some lengthy work done on her right foot. It appeared a blister on her big toe was the culprit.

Soon enough, Wozniacki was back on court, buzzing like a bumblebee. She hit a well-crafted forehand that Kerber couldn’t quite run down and broke the German for the third time to take the set.

Wozniacki jumped out to a 2-0 lead in the second set when she broke Kerber for a fourth time. At 4-1, it was Kerber who called for medical attention -- for an ailing back.

It was over when Kerber sent two tired backhands into the net. The two embraced at net and shared a laugh. It probably won’t be the last one.