Three-time Miami Open winner Victoria Azarenka battled for nearly three hours to get past a determined Yulia Putintseva and take her place in the semifinals with a 7-6 (7/4), 1-6, 6-3 win on Tuesday.
Fourth-seeded Elena Rybakina, the highest-seeded player left in the tournament, held off a strong challenge from eighth-seeded Maria Sakkari of Greece before emerging with a 7-5, 6-7 (4/7), 6-4 win.
The 34-year-old Azarenka, who won in Miami in 2009, 2011 and 2016, had to deal not only with the spirited display from the Moscow-born Kazakh player, but also a long disruption to the match due to a technical problem.
The match was stopped for 45 minutes in the fourth game of the first set due to a power outage which impacted the umpire's communications and the Hawkeye system.
Azarenka had to save three set points on Putintseva's serve at 5-4 in the first set, then missed out on two set points of her own at 6-5 before the tie-break.
Putintseva dominated the second set but Azarenka found the strength to get ahead in the third but still her opponent refused to relent, fighting off match point before breaking.
But Azarenka held on her next serve to secure passage to the last four and keep alive her hope of a fourth Miami title.
"Yulia played great, she's in such great form and I really had to dig deep. I felt like my legs were kind of giving in a little bit and I lost a little bit of self-belief because she was playing so well and moving me around everywhere," said Azarenka.
"But I'm happy that I was able to regroup, reset and really take my chances, come out and play aggressive and face the challenge," she said.
Azarenka said the win showed that there can be no doubt about her desire to compete at the highest level.
"I'm motivated to compete and go after my dreams. I've been playing on tour for 20 years and I still feel like I am improving, that's priceless for me and I want to keep going," she added.
RYBAKINA'S EPIC BATTLE WITH SAKKARI
Belarusian Azarenka will face Rybakina for a place in the final.
Rybakina, at 24, is the youngest player left in the tournament and she needed all her energy to survive a 2hr 48min tussle with Sakkari.
Rybakina led 6-5 in the first set and the match looked poised for a tie-break but Sakkari's service game deserted her at the crucial moment and she was broken with a fine down-the-line winner from the Kazakh, last year's beaten finalist in Miami.
Sakkari opened up a 4-2 lead in an error-strewn second set but allowed Rybakina to win the next three games and had to save two match points.
The Greek ran out the winner in the tie-break but Rybakina, who looked to have an ankle problem, was able to finally break at 3-3 converting on her third break point.
Sakkari's determination saw her save four match points when 5-3 down as she held but this time Rybakina was able to close out the contest on her serve.
"It was such a tough battle, as it has been before. I am really happy but now I just need to recover," said Rybakina.
World No 1 Iga Swiatek, Aryna Sabalenka and third seed Coco Gauff have all been eliminated.