Simona Halep of Romania celebrates after defeating Polona Hercog of Slovenia on Day 7 of the Miami Open Presented by Itau at Hard Rock Stadium on March 24, 2019 in Miami Gardens, Florida
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Hercog, ranked 93rd in the world, pushed Halep all the way in the second set but the Romanian dominated the tiebreak to turn the match around and eventually triumphed 5-7 7-6(1) 6-2.
She will face three-time Miami Open champion Venus Williams in the fourth round after the American beat Russian 14th seed Daria Kasatkina 6-3 6-1.
World number three Halep avoided becoming the third major player to exit the tournament in two days.
Japanese world number one Naomi Osaka was stunned by 27th seeded Taiwanese Hsieh Su-wei while Serena William was forced to withdraw with a knee injury earlier on Sunday.
Two other seeds went out on Sunday.
Latvian 11th seed Anastasija Sevastova lost 1-6 6-2 6-3 to Kazakh Yulia Putintseva and 25th-seeded American Danielle Collins went down 7-5 6-1 to China's Wang Yafan.