All in the biomechanics: modified serve propels Aryna Sabalenka back to US Open semifinals

The word “flat” cuts two ways in tennis. A flat ball can often be quite effective, particularly when it goes deep into a corner. Call that the sunny upside of flat. Today, in a quarterfinal match at the US Open, sixth-seeded Aryna Sabalenka personified this definition of flat.

Then there is the downside: a player lacking the energy needed to hit the ball with any kind of sustainable force, purpose or consistency. That was how things started today for 23th-seeded Karolina Pliskova.

It proved a workable combination for Sabalenka, who earned a 6-1, 7-6 (4) victory to reach the US Open semis for the second year in a row.

These two had previously played one another four times, each winning twice. Three of them have gone three sets, their battles marked by one laser-sharp drive after another, a narrow level of margin that also makes for considerable streakiness.

Today, though, the mix of an inspired Sabalenka and a listless Pliskova threatened to turn this into a rout. Perhaps still weary from the 182-minute three-setter she’d won over Victoria Azarenka in the previous round, Pliskova through those early stages repeatedly flung balls long and, in even more dispirited fashion, lined many into the net.

As much as any top player you’ll ever see, Pliskova has an extremely limited range of tactics. You won’t see her loft a ball high. Though Pliskova’s a fine volleyer, she rarely comes to net. Nor does she vary speed and spin much on her serve. It’s a style that’s taken her to two Grand Slam finals and many more results. But for much of today’s match, the overall gloom of it all matched the overcast sky that loomed over Arthur Ashe Stadium. Said Pliskova, “I guess there are days like this when you know she's playing amazing, I'm not playing the best, not serving the best at all today. Just somehow couldn't feel really the court. I was a bit lost out there.”

Propelled by forceful serves and one concussive groundstroke after another, Sabalenka swept through the first four games and handily took the first set in 28 minutes. Fittingly, with Pliskova serving at 1-5, ad out, Sabalenka closed out the set with an untouchable down-the-line forehand return. During that time, Pliskova had hit one winner and 15 unforced errors, Sabalenka 10 of each. Said Sabalenka, “Yeah, I think I start really well, and the first set was really high level for me and put a lot of pressure on her. Yeah, first set was really great.”

Credit Pliskova for a moderate energy upgrade that kept her close to Sabalenka all through the second set. Serving at 3-4, 30-40, she laced a backhand down-the-line to extract an error and soon held for 4-all.

But when it came to the return game, Pliskova was unable to attain any traction. Sabalenka’s serve was impeccable—seven aces, only one double-fault, a whopping 63 percent of second-serve points won and not once facing a break point. “She was serving amazing,” said Pliskova. “There was not really many chances how I could start to play better.” This represents a major breakthrough, as Sabalenka has struggled extensively with her serve in recent times. Sabalenka gave credit for that improvement to work she’s done recently with Gavin MacMillan, a biomechanics expert.

And yet, for all Sabalenka’s early dominance, once that second set reached 6-all, who could tell which way momentum would swing? Rare as it is to see Sabalenka be the player with more margin on her groundstrokes, the world has often enough seen balls fly off her frame in all directions. Meanwhile, Pliskova, never one to reveal much of anything, stood seven good points away from levelling a match she’d begun so poorly.

But just like the sky, Pliskova was unable to find the sunshine. Still, serving at 2-4, to win that point would force Sabalenka to serve at 4-3. And given Sabalenka’s prior troubles with the serve, perhaps there’d be a breakdown. But instead, mid-rally, Sabalenka feathered the first drop shot of the match, a deft down-the-line backhand that gave her just enough of a cushion to eventually close out the tiebreaker, 7-4. Fittingly, the final shot was a down-the-line forehand return winner.

The freshness Sabalanka brought to this match might well be a byproduct of her not having Wimbledon and instead spent that time in Miami. If the bad news was that she was unable to compete at a tournament where she’d lost a year ago in the semis, the good news was a chance to enhance her skills. “Yeah, it was tough time,” said Sabalenka, “especially when I was working out in the gym and there was Wimbledon playing on the TV. I was always turn it off because I couldn't watch it. But it was tough time, and I worked so hard. Yeah, I worked a lot in that period.” So far, the work appears to be paying off.