Ash Barty wasn't her usual easy-going self after struggling through a three-setter into the quarter-finals of the China Open. But there's a far bigger potential source of frustration awaiting her tomorrow...Petra Kvitova.
For her part, world number seven Kvitova has breezed into the quarterfinals without dropping a set, defeating tough French customer Kristina Mladenovic 6-4, 6-4 and accounting for Belinda Bencic 6-3, 6-3.
They're both experienced campaigners that tend to hang around the edge of seedings for Grand Slams and can claim a few scalps throughout the season, but they're a step below Barty and Kvitova will need to assume some edge, quickly.
On Kvitova's side is experience. She's beaten Barty four times to the Australia's one win so far throughout her career, with the Czech Wimbledon champion proving too intimidating for Barty on recent occasions.
Barty had a strong start to the Chinese Open, easily beating another of Kazakhstan's growing slew of contenders, Yulia Putintseva, but it got a lot tougher - as it always has recently - with hometown favourite Saisai Zhang.
Barty admonished her own performances in that second set, before eventually progressing 6-3, 6-7, 6-2.
“I played a pretty stupid set. I made probably over 20 errors in that second set, and cheap ones in rolls, in twos and threes in a row, which is disappointing. Not things that I like to do,” Barty assessed post-match.
“Let her back in the match well and truly.
“I think too many times I gave away cheap service games. When I did have my opportunity, I didn’t take it.
“I just had to reset (in the third). I had to know that the match was well and truly on my racquet. Happy with how we were able to respond in that third set. Overall, a frustrating night.
“But the beauty of this sport is that we’re still alive in the tournament. I’ve kind of got a fresh day come Friday (against Kvitova) where it can be a completely different game.”
It's a different tone than we're used to seeing with the world number one. She sounds like she's feeling the pressure and she's playing like it, to.
But a set of tennis is always worth a thousand words, so we'll get the best account of how she's performing since the US Open when she faces Kvitova tomorrow.
Sabalenka was always going to be a tough ask, her game naturally counteracts Barty perfectly and when she's on-form she's a danger player for anybody on tour, one of those you definitely don't want to face in a final.
But Kvitova is far more measured, predictable, known.
She's experienced, Barty knows how she'll play and Kvitova won't get in Barty's face or blast her off the court - she'll simply beat her with an all-round consistent game if Barty's mind is an inch off that hard Beijing surface.
And then we'll know more certainly than we have in months, whether everything's truly alright at the top.