For the first time in six tries, Madison Keys toppled a reigning World No.1. The unseeded former champion knocked out top seed Iga Swiatek in the third round of the Western & Southern Open on Thursday in straight sets, 6-3, 6-4.

Here are three takeaways from Keys' big win, which first looked easy and got tight late, that puts her in the quarterfinals in Cincinnati for a third time in her career. 

For the first time: Not only did Keys enter the match 0-5 in her career against World No.1 players, but she'd also never won a set. She was also 0-2 previously against Swiatek, including a 6-1, 6-0 defeat in the quarterfinals of the BNP Paribas Open that lasted less than an hour. 

"It feels great," Key said afterward. "I obviously have not had the best success against World No. 1s, so being able to get a win against Iga, especially after having two losses to her already, means a lot to me, and I think I'm playing some pretty good tennis."

Ten in a row, until: Keys won 10 games in a row in the middle of the match after Swiatek led 3-2 in the first set. The first six games went with serve -- in which Keys erased the only break point either player faced, in the fourth game -- and soon found herself ahead, 6-3, 5-0. 

It was then that things got complicated. Swiatek saved a match point to save the bagel and won 11 of 12 points to tighten the scoreboard to 6-3, 5-3. The top seed saved another match point in the ninth game and broke Keys again to get the second set back on serve. 

But Keys reset admirably when it mattered most. Thanks in part to two more groundstroke winners, Keys broke Swiatek's serve for a fifth time, and converted her fourth match point.

"I was really just thinking that I had to focus a lot on why I got in the position of being up 5-Love," Keys said. "I think I backed off a little bit, and I think she started playing better.

"I just knew that I was going to have to try to put some pressure on her early in the game just to kind of also make her aware of the situation. All of a sudden it's 5-4 and she feels like she has to hold that game. So just really trying to swing at the ball, make sure I was moving my feet, and put as much pressure on her as quickly as possible."

Big hitting blasts Keys through: Though both players made 14 unforced errors in 85 minutes, Keys hit more than twice Swiatek's total of winners (14 to 6). She also created 14 break point chances against Swiatek's serve.

Most notably though, Keys handed the World No.1 her second third-round defeat in a row after she was beaten by Brazil's Beatriz Haddad Maia in Toronto last week. Swiatek is now just 4-4 since her 37-match winning streak ended at the hands of Alizé Cornet at Wimbledon.

Elena Rybakina into first quarterfinal since Wimbledon

Through three matches, World No.25 Elena Rybakina has not lost a set in Cincinnati, and moved through another straight-set victory, this time 6-2, 6-4 over Alison Riske-Amritraj to also reach the quarterfinals.

In wins over Mayar Sherif, Garbiñe Muguruza and Riske-Amritraj, Rybakina has lost more than three games in a set just once. 

Rybakina has struck a tournament-leading 22 aces en route to the quarterfinals, an average of over seven aces per match. She fired nine against Riske-Amritraj and faced just one break point in the match while dominating from the baseline. 

Rybakina is bidding to make the first WTA 1000 semifinal of her career, and she'll have to beat Keys for the first time to do it. At Roland Garros in May, Keys came from a set down to triumph in the pair's first career meeting in a deciding tiebreak 3-6, 6-1, 7-6[3].