No 1 seed Aryna Sabalenka of Belarus was among the seeded players to start the Mutua Madrid Open with straight-sets wins in Spain.

Following a first-round bye, Sabalenka topped Russia's Anna Blinkova 6-3, 6-4 on Friday.

Sabalenka won 27 of 36 first-service points (75 percent) and saved six of seven break points.

She said before the tournament that she is working to add more finesse moves to a game currently ruled by her power.

"It's a learning process and I'm not afraid to make mistakes," Sabalenka said.

"I think with time I will learn how to make the right decisions. It's going to benefit my game.

"I think on the clay court [of Madrid], it's like a good practice with those shots. You just have to make sure you pick the right one at the right moment."

American third seed Jessica Pegula needed just 72 minutes to defeat Germany's Eva Lys 6-2, 6-2.

Pegula, who saved six of eight break points while converting six of 10 opportunities to break Lys, could rise to No 2 in the world rankings for the first time depending on the results of this WTA 1000 tournament.

Five seeded players were knocked out on Friday, with the biggest upset belonging to Russia's Anastasia Potapova, who dismissed eighth-seeded Zheng Qinwen of China 6-4, 6-4.

"This win doesn't feel crazy and something out of this world," Potapova said, "only because the last matches that we played it was such a battle, always the tiebreak was involved, over three hours. Maybe this gave me the feeling that I'm actually on the same level as her."

Also, Peyton Stearns outlasted No 15 seed Amanda Anisimova 6-2, 2-6, 7-5 in an all-American battle; Switzerland's Rebeka Masarova beat No 22 Yulia Putintseva of Kazakhstan 6-3, 6-3; Japan's Moyuka Uchijima toppled No 26 Ons Jabeur of Tunisia 4-6, 6-3, 6-4; and Greece's Maria Sakkari edged No 29 Magda Linette of Poland 7-6 (5), 6-3.

Italian sixth seed Jasmine Paolini defeated Great Britain's Katie Boulter in an hour flat, 6-1, 6-2.

No 10 Elena Rybakina of Kazakhstan turned back Canada's Bianca Andreescu 6-3, 6-2.

Other winners included No 17 seed Elina Svitolina and No 24 Marta Kostyuk, both of Ukraine; No 14 seed Daria Kasatkina of Australia; No 21 seed Ekaterina Alexandrova of Russia; No 28 seed Elise Mertens of Belgium; No 32 seed Sofia Kenin of the United States; and Russian Veronika Kudermetova. (Reuters)