It was literally a contest of Czech left-handers, and two-time Wimbledon champion Petra Kvitova wasn't ready for it on Wednesday in the second round of the Volvo Car Open on Daniel Island.

The lesser-known, lesser-feared of the Pliskova twins, Kristyna, was more ready on this day than Kvitova, although it might not have appeared that way when Kvitova waltzed through the first set. The last two sets were all Pliskova in a 1-6, 6-1, 6-3 upset of the tournament's No. 2 seed.

And then, there was Fanny Stollar.

Stollar, a qualifier, has shaken things up again in the VCO main draw. The hard-hitting 19-year-old Hungarian has advanced to the tournament's round of 16 for a second straight year.

Stollar did it this time with an impressive 6-3, 6-4 win over No. 6 seed Johanna Konta as the Volvo Car Stadium crowd must have wondered what's next. The match never really got tight as Stollar easily outplayed her No. 219 world ranking.

Konta's stay was brief this time. She was the No. 2 seed a year ago, but withdrew with an injury.

Crowd favorite Madison Keys gave the night crowd a treat as the spell of upsets in the stadium ended, but not before 2016 runner-up Keys was pushed to a third set. Keys, the seventh seed, pulled out her big serve and follow-up blistering ground strokes to hold off Spaniard Lara Arruabarrena 6-1, 3-6, 6-3 to earn her spot among the final 16 against Italian Camila Giorgi.

In the battle of Czech left-handers, Pliskova looked out of place on clay in the first set, and Kvitova returned the favor the rest of the match. The serve warmed up for the 6-0 Pliskova in the second set, and she even out-rallied the 10th-ranked Kvitova quite often. Kvitova also tossed in nine double faults.

It was the second top 10 win of the year for the 77th-ranked Pliskova, who came to Charleston with only four wins on the year. Kvitova leads the WTA Tour with six wins this year against top 10 players.

"The match is big for me, but I am not surprised," said Pliskova, who said she received tips from her 2016 U.S. Open runner-up sister, Karolina, on how to play Kvitova on clay. "I'm not really surprised because I know how I can play."

But she isn't exactly expecting to win the tournament. Indeed, "I would be surprised if I won the tournament."

Pliskova will draw 16th seed Elena Vesnina of Russia in Thursday's round of 16, and she plans to ask her sister how to play 2011 VCO finalist Vesnina for the first time in singles.

"I think she (Karolina) has played her, so she will give me some advice. But the key for me is serve and to play aggressive," Pliskova said.

What was the difference against Kvitova? "The first set was horrible and that's the biggest difference, and of course she missed a couple of times, and I just played aggressive more," Pliskova said.

Stollar was just happy to keep her success going at the VCO. "I honestly can't tell you what it is," she said. "I just feel pretty good here and relaxed and you're just enjoying it here."

She had no superstitions about her good luck in Charleston. "Just in Charleston, I'm just really relaxed. I'm just going to do the same thing every day."

Playing without a coach these days, how did Stollar upend the highly regarded Konta? "I think I pushed my game to her and I stayed really aggressive. I could push her back behind the baseline," Stollar said.

Naomi Osaka is making things look easy this week with her awesome power. Just like Jennifer Brady in Osaka's first-round win, Laua Siegemund made a good run at the tournament's 10th seed.

But the 20-year-old from her name sake Osaka, Japan, just had too many weapons for the plunky drop-shooting Siegemund, who wore a large support on her right knee. Osaka is just too good, too quick and too strong for most of the women in this year's VCO.

If it comes down to a service game, count on Osaka to impose her will and strength on the ball in Serena fashion, like at match point in her 6-3, 7-6 (8) win over Siegemund.

Siegemund wasted four set points in the second set. The first one came against Osaka's serve in the 10th game, and Siegemund had two more against Osaka's serve in the 12th game. Osaka got out of all three with huge serves.

Another Siegemund set point came in the tiebreaker, which Osaka ended on the 18th point, of course, with an ace.

Osaka will face fifth seed Julia Goerges of Germany in the round of 16.

A sleeper in the crowd of 16 is 2011 French Open runner-up Sara Errani, probably the most true clay-courter in the tournament. A wild card, the 5-5 Italian upended 15th seed Mihaela Buzarnscu of Romania, 3-6, 7-6 (5), 6-2, out on the Althea Gibson Club Court. She will face American Bernarda Pera in the round of 16.

Another player to watch is Ashleigh Barty of Australia, the ninth seed who has come out of nowhere the last couple of years to move up to 18th in the world. Barty is a master of the one-hand backhand and wonderful backhand slice that she used to conquer Tatjana Maria of Germany, 4-6, 6-3, 6-2, on an outside court.

If you're looking for another possible upset, a good place to watch might be defending champion Daria Kasatkina's Thursday match against tall, hard-hitting Irina-Camelia Begu of Romania, the 13th-seed who overpowered reigning Junior French Open champion Claire Liu, 6-4, 6-2, in the second round.

Reach James Beck at jamesbecktennis@gmail.com.