Punching or counterpunching power remains essential. Barty and Andreescu, who will face Elise Mertens in the quarterfinals, have the big forehands and strong serves to hit winners on their own (Andreescu also has a deadly crosscourt backhand). But they have the court-coverage skills to absorb pace along with tactical and technical variety.

It is quite a package.

“Players like Osaka are going to be forced to add more variety to their game,” said Sven Groeneveld, one of the game’s most experienced coaches, who worked with Maria Sharapova and most recently Sloane Stephens.

Barty, the Australian who won the French Open this year and will return to No. 1 on Monday, has perhaps the best volleying technique on tour along with a crisply sliced backhand. Andreescu, the Canadian who won hardcourt titles in Indian Wells and Toronto this year, is also happy to express herself on all sections of the canvas. She is a potential No. 1 herself if she can avoid the types of injuries that have slowed her progress so far.

“Look, I’m not sure we can say yet that there is a change in women’s tennis,” Sylvain Bruneau , Andreescu’s coach, said in an interview on Sunday. “I think it would be nice, but it might be a bit early to call it a big trend. But as far as Bianca is concerned, there is definitely a desire on her side to play tennis in a way where she’s using different tools, different strategies and keeping things versatile and mixing things up. It’s how she likes to play tennis and how we train, and it’s possible that it will influence others to do so. But let’s wait and see.”

The wait may not be long. Consider the tactics deployed by the 17-year-old American Caty McNally when she pushed Williams to three sets in the second round at Ashe Stadium. She served and volleyed on only a few occasions, but she also hit flat returns off Williams’s second serves that she followed to net.

Her results were mixed, and she lost the final two sets in a hurry. But it was revealing that she felt confident enough to deploy her attacking skills on that grand a stage against a champion of Williams’s stature.

“My mom played a lot of doubles in her career, and I’ve worked on volleying ever since I was really young,” said McNally, whose mother, Lynn, played at Northwestern and briefly on the WTA Tour. “I think that’s something that other people don’t do. They just kind of are more baseline-oriented, and for me, I’m always working on my volleys every single day.”