For 19-year-old Eala, the upset third-round victory over the American fifth seed extended her dream run in Miami where she has now toppled two Grand Slam champions having beaten 2017 French Open winner Jelena Ostapenko in the second round.
Eala, who has trained at Rafa Nadal's academy in Mallorca since she was 13, required a medical timeout for what appeared to be a leg injury but was a force from the baseline against Keys, who reached the Indian Wells semi-final last week.
Up next for Eala will be Spanish 10th seed Paula Badosa, a 6-3 7-6 winner over Dane Clara Tauson.
In other matches, Former champion Iga Swiatek earned a 7-6 6-1 win over Belgian 27th seed Elise Mertens that put the Polish second seed into the last 16 and made her the first player to reach the last 16 of a WTA 1000 event in 25 consecutive appearances.
Swiatek built a seemingly comfortable 5-2 lead in the first set but Mertens managed to claw back to 5-5 before the Pole ran away with the tiebreaker and breezed through the second frame.
"I'm happy that I got my level up in the tiebreaker to close it in two sets," Swiatek said.
"Also in the second set I felt like I was playing good, big confidence.
"Yeah, overall I'm happy with the performance and how I worked through some issues."
Up next for Swiatek will be Ukrainian Elina Svitolina, who beat Czech 15th seed Karolina Muchova 6-2 3-6 6-2 and is looking to build on her run to the Indian Wells quarter-final where she lost to eventual champion Mirra Andreeva.
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