Australian Open champion Elena Rybakina fell to a shock 7-6 (10/8), 6-4 defeat by Anastasia Potapova on Monday in the Madrid Open fourth round.
Earlier world number one Aryna Sabalenka overcame Naomi Osaka 6-7 (1/7), 6-3, 6-2 in a gripping battle to reach the quarterfinals.
Third seed Coco Gauff was eliminated in a three-set battle with Linda Noskova decided on a final set tie-break in an exciting fourth-round clash.
Sabalenka, who has claimed titles at Miami, Indian Wells and Brisbane this year, was tested by her Japanese opponent but came back from a set and a break down to triumph.
"I'm really happy that I didn't give up and I was pushing until the very last point," said Sabalenka on court.
She later told reporters: "When (she) put me under pressure, I was able to pull out really incredible shots and incredible tennis. So I'm happy."
The first set between the two four-time Grand Slam winners was tight, with only one break point forced, by Sabalenka, which Osaka saved to hold for 2-1.
Bringing her A-game 💯@naomiosaka takes the first set against Sabalenka 7-6(1)!#MMOPEN pic.twitter.com/BL0uTrg737
— wta (@WTA) April 27, 2026
Osaka dominated in the tie-break, ripping into a 5-0 lead and then triumphing when Sabalenka lashed a return wide.
Reigning champion Sabalenka stepped up a gear in the second frame, although world number 15 Osaka dug deep to survive three break points and then managed to engineer a break for herself to take a 2-1 lead.
However, the Belarusian immediately broke to love and then again in the eighth game, serving out to take the second set.
150th WTA 1000 win! 🫰@SabalenkaA | #MMOPEN pic.twitter.com/sH0UjAwQjF
— wta (@WTA) April 27, 2026
Only Rybakina has beaten Sabalenka this year, in the Australian Open final, and the 27-year-old dominated in the third set, securing breaks in the fifth and seventh games while Osaka could not put pressure on her opponent's serve.
Sabalenka sealed her victory by serving to love with an ace to reach the last eight, where she will face American Hailey Baptiste, who beat Belinda Bencic in three sets, including losing a tie-break 16-14 in the second.
Osaka said she was happy with pushing Sabalenka to the wire after going down in straight sets when they met at Indian Wells.
"I feel like every game was super close. I think... I could potentially match her in power," said Osaka.
"I feel like in Indian Wells I was a little overwhelmed. Here I did a little bit better.
"Obviously she's the No 1 player in the world, so it was a really cool match for me to know that I'm kind of there."
World No 3 Gauff, who had been dealing with a stomach bug this week, fell to a 6-4, 1-6, 7-6 (7/5) defeat by Noskova.
The Czech earned a decisive break in the fifth game of the first set, but American Gauff secured two of her own to claim the second.
New territory in Madrid unlocked 🔓
— wta (@WTA) April 27, 2026
Linda Noskova takes out the No.3 seed Gauff for a place in the quarterfinals!#MMOpen pic.twitter.com/Wb6svCT7et
Gauff moved two breaks up in the third but let the match slip away from her as Noskova pulled back to level 4-4.
The American led 3-0 in the tie-break before again she could not hold on.
In the day's late match Kazakhstan's Rybakina, the world number two, was shocked by her 56th-ranked opponent.
Both players secured two breaks in the first set before Potapova edged Rybakina in the tie-break.
In the second set Rybakina captured her fifth break point of a long fifth game to nose ahead but lost the eighth and 10th games as Potapova triumphed.
"I'm speechless, I'm extremely happy, it was such a tough match and tough opponent," said Austria's Potapova.
"My team helped me today, they were there for me, big thanks (to them)."
UPSET ALERT in Madrid 🚨@nastiaapotapova advances to the quarterfinals after defeating Rybakina in straights 7-6(8), 6-4!#MMOPEN pic.twitter.com/dcPM8DRfxm
— wta (@WTA) April 27, 2026