There were mixed fortunes for seeded players on Wednesday at the Mubadala Silicon Valley Classic.
In the day session, No.4 seed Daria Kasatkina rallied from a set down to beat Caroline Garcia in a clash of former Top 10 players, 3-6, 7-5, 6-3, while No.6 seed Petra Martic and No.7 seed Alison Riske were beaten by Poland's Magda Linette and qualifier Ana Konjuh, respectively.
Two games away from a straight-sets defeat in the second set, Kasatkina later rallied from 3-1 down in the decider to even her career head-to-head against Garcia at 1-1.
"It was a tough match. From my point of view, I think the level of the game was very good, and I'm really happy that I was able to turn the match in the second set," Kasatkina said in her on-court interview.
"Caroline was serving really well, so it was tough. The balls kept bouncing high so it was tough to return, but I was really happy that I was able to find a way to do it.
"Sometimes, the main adjustment is to just put the balls inside the court. This is everything you're trying to thing about. It's one more, one more, one more. It doesn't matter how. It's important to just put the ball inside the court, and try to deal with what you get.
"I'm very proud... I'm coming to the tournaments to go further and further, so I'm happy to be in the quarterfinals and already looking forward to my next match."
While Kasatkina managed to avoid a second round upset, the same could not be said for Riske and Martic, each of whom were beaten in straight sets.
Linette kicked off the the day with a 7-5, 7-6(5) win over Martic, in which the World No.45 was a break down early in the first set, and 3-1 and 5-3 down in the second set tiebreak.
Having beaten Martic in three sets in each of their previous meetings, however, the Polish No.2 managed to avoid being taken the distance for a third time by winning the last five points of the match.
"She's very tough. She serves so well, so you feel immediately that you need to do really good on your serve," Linette said after the match.
"In the second set, I thought that I just wanted to be as solid as I could be in my service games, but she pulled off some great shots. It was really, really tough.
"I knew would need to try to be a little bit more aggressive today, to be the one who dictated the points more... it's the first time that I'm into the quarterfinals of a WTA 500 so I'm very excited and I'm playing pretty well, so I'm really happy."
To keep a perfect head-to-head record against the Croatian at 3-0, Linette struck 27 winners to 25 unforced errors in the 1 hour, 52-minute victory, nearly doubling Martic's 15 winners.
In other news for Croatian tennis, former Top 20 player Konjuh reached her first WTA 500-level quarterfinal in four years with a 6-1, 6-4 win over Riske, a fourth victory so far this week.
The current World No.116 won five games in a row with ease in the opener, dropping just three points on serve, and earned the decisive break early in the second set.
In the night session, China's Zhang Shuai extended her career mastery over Madison Keys with a 7-5, 7-6(5) upset of the No.3 seed, improving her all-time head-to-head record against the former US Open finalist to 5-2.
"Today was a great match for both of us. Madison is a great player and I had to play my best tennis. I think we're both fighters, and that's why we always play close, very tough matches," Zhang said in her on-court interview.
"I didn't think too much about my opponent. I just thought about myself, tried my best and worked on what we practiced and improved... with my coach. The last few weeks for me were very tough, and I want to continue."
Zhang came from 3-0 down in the second set to close out the 1 hour, 41-minute victory, extending a track record of success against the American that dates back a decade.
The World No.51 could not convert two set points on serve at 5-3 in the opener, nor a match point at 5-4 in the second, but rose to the occasion later in each set before securing victory on her third match point.