BEIJING, China -- Sorana Cirstea of Romania claimed her first victory against a Top 5 player in over four years when she upset Czech No.4 seed Karolina Pliskova, 6-1, 7-5, in the third round of the China Open on Thursday.

"I didn’t think about her ranking, I just focused on my game today," said Cirstea during her post-match press conference. "I’ve been playing well lately, it’s just that probably results didn’t come as quick as I hoped. But I was working well lately, and doing the right things, and I always say that hard work will pay off in the end."

Pliskova and Cirstea had played only once before, with the Czech coming from a set down to claim a three-set victory back in 2014. But the unseeded Romanian turned the tables in Beijing, winning the final five games of the match to advance in 83 minutes.

"My coach told me that I was down 5-2, 40-0 in the second set, and I didn’t even realize it," Cirstea exclaimed. "I was just playing point by point, I was trying not to focus on the score. I was just trying to play the right ball at the right time."

"And I think for me it worked, because I didn’t put any pressure on myself," Cirstea continued. "It didn’t feel like a comeback because I was not so aware of the score. But it was definitely nice to finish in two sets."

Cirstea was impressive from all corners of the court, including winning nearly 70 percent of the points off of her first serve. Neither player was effective off of their second serves, but Pliskova had a particularly rough day serving, which included getting only 44 percent of her first serves in.

In the first game, Cirstea quickly went down triple break point, but utilized aggressive play to reach deuce. The game quickly turned into a marathon, with two game points going by the wayside before Cirstea hit her sixth unforced error of the game on Pliskova’s fifth break point.

Cirstea completely turned the set around after that game, breaking right back for 1-1 in a game where Pliskova offered up three double faults. Starting there, the Romanian reeled off six straight games, including three breaks of Pliskova’s serve, en route to a 6-1 lead. 

Cirstea only hit one unforced error in that six-game run, while Pliskova capitulated with 17 unforced errors in the set, and failed to win any of her nine second service points in the opener.

The momentum shifted Pliskova's way at the beginning of the second set, as she started to find the court more frequently with her powerful groundstrokes. After holding serve for the first time in the match to lead 1-0, Pliskova broke for 2-0 off of a forehand return winner.

Cirstea got the set back on serve at 3-2 after Pliskova double faulted down break point. But Pliskova quickly reclaimed the break advantage in the next game after multiple unforced errors from the Romanian World No.44 caused her to cede her service game at love.

After Pliskova easily held for 5-2, Cirstea looked rattled. She quickly went down triple break point, giving the Czech three set points, and a chance to send the match into a decider. However, some inexact returning from Pliskova allowed Cirstea to escape that service game and force Pliskova to serve out the match at 5-3.

Pliskova, the WTA ace leader for the season, used one of those bombs to get to a fourth set point, but it went awry when she hit a backhand unforced error wide. Pliskova then hit another double fault when down break point, to put the set back on serve at 5-4.

Suddenly, it was Cirstea who looked the more confident of the two, prolonging points with exceptional scrambling and deploying her power game when necessary, including an ace to hold for 5-5.

Another backhand unforced error by Pliskova gave Cirstea a chance to serve out the match at 6-5, which she did with aplomb to complete her five-game run to the upset.

In the quarterfinals, Cirstea will play her current doubles partner, No.9 seed Jelena Ostapenko of Latvia, who moved on when Chinese No.1 Peng Shuai had to retire due to injury while trailing 3-0. Ostapenko beat Cirstea in their only meeting, in the second round of this year's US Open.

"She’s a great player; she’s been playing really, really good lately, especially here in Asia," Cirstea said, regarding Ostapenko. "Again, I have to bring my best tomorrow, and to try and play my game aggressive, and at the end we’ll see who’s the better one."