Russian qualifier Varvara Gracheva overpowered fourth-seeded Ons Jabeur of Tunisia 6-2, 6-2 on Friday in the second round of the Miami Open.
Jabeur, who is ranked fifth in the WTA, twice sought assistance from the training staff. She has been slowed by a knee injury this year, perhaps playing a role as Gracheva beat a player ranked in the world top five for the first time.
Gracheva said: "The plan was, of course like all matches, to be as stable as possible, to try to make her work as much points as possible, and of course wait for comfortable ones to attack."
Gracheva wound up saving three of the four break points she faced while converting five of her six break opportunities.
"I just probably caught this wave where I'm stable, where I always have a chance to play my game, be aggressive, cause troubles for the others by the game style," Gracheva said. "Just try to keep rolling on this way."
Two other highly seeded player joined Jabeur on the way out of Miami, as No. 5 Caroline Garcia of France and No. 7 Maria Sakkari of Greece both lost their second-round matches.
Romania's Sorana Cirstea cruised past Garcia 6-2, 6-3, while Canada's Bianca Andreescu overtook Sakkari 5-7, 6-3, 6-4.
Andreescu said of her victory, "I think the match was really good from both of our parts. Maria played amazing. She was playing very aggressive.
"I felt like I was on my heels a lot of the time during the match, but I made every ball. I fought to the end, and I think I played the important points just a little bit better today. But, yeah, it could have gone either way today."
Second-seeded Aryna Sabalenka of Belarus produced a 6-4, 6-3 win over the United States' Shelby Rogers. Ninth-seeded Belinda Bencic of Switzerland demolished Canada's Leylah Fernandez 6-1, 6-1, but 11th-seeded Veronika Kudermetova of Russia fell 6-4, 6-2 to Czech Republic's Marketa Vondrousova.
Other second-round winners were 15th-seeded Petra Kvitova, 16th-seeded Barbora Krejcikova, 17th-seeded Karolina Pliskova, 31st-seeded Marie Bouzkova and Karolina Muchova of the Czech Republic; 18th-seeded Ekaterina Alexandrova of Russia; 19th-seeded Madison Keys and Sofia Kenin of the United States; 22nd-seeded Donna Vekic of Croatia; and Magdalena Frech of Poland.