Rome - Japan's Naomi Osaka won twice on Thursday to reach the Italian Open quarter-finals, retaining the world number one ranking ahead of the start of the French Open next week.
She eased into the last eight in Rome with a 6-3, 6-3 win over Mihaela Buzarnescu.
Osaka beat the 29th-ranked Romanian in 78 minutes after earlier beating Slovak Dominika Cibulkova by the same scoreline in one hour and 42 minutes in the second round, as players doubled up after the previous day was washed out.
At the start of the day, the 21-year-old had needed to make the quarter-finals to ensure Romanian Simona Halep could not swipe the number one ranking and with it top seeding in the French Open.
But Osaka's top spot was guaranteed when reigning Roland Garros champion Halep fell to Czech Marketa Vondrousova 2-6, 7-5, 6-3 in the second round.
"I have to think about winning tournaments. That's sort of what I've been thinking about this entire tournament," said Osaka.
"Of course, it's a relief (to be top seed at Roland Garros) because that definitely was a very big goal of mine."
Osaka next meets Madrid Open champion and sixth seed Kiki Bertens for a place in the final four.
The two players have met twice before, but never on clay, with Bertens winning at the WTA Finals last year to avenge a straight sets loss to the Japanese star in Acapulco in 2016.
Osaka, who broke through by winning the US Open last year and Australian Open this year, did not survive the second round in her two previous appearances in Rome.
Before this year Osaka had never made the last eight of any clay tournament, but has now also reached the semi-finals in Stuttgart and quarter-finals in Madrid as she warms up for the French Open start on May 26.
With a game often pigeon-holed as ideal for harder courts than clay, Osaka insists she is getting used to the slower European surface.
"One of the biggest things is instead of complaining about it, I'm just trying to figure out how to adapt to it. This is, like, an inevitable part of the season.
"This is the clay season, I can't just skip this entire swing. I also feel like I want to be a player that's great on all surfaces. I think one of the biggest steps is, of course, starting to do well on clay, learning how to adapt."
Results from the ATP and WTA Italian Open tournaments in Rome on Thursday (x denotes seeding):
Novak Djokovic (SRB x1) bt Denis Shapovalov (CAN) 6-1, 6-3
Philipp Kohlschreiber (GER) bt Marco Cecchinato (ITA x16) 6-3, 6-3
Casper Ruud (NOR) bt Nick Kyrgios (AUS) 6-3, 6-7 (5/7), 2-1 - disqualified
Juan Martin del Potro (ARG x7) bt David Goffin (BEL) 6-4, 6-2
Diego Schwartzman (ARG) bt Albert Ramos (ESP) 7-6 (7/5), 6-1
Jan-Lennard Struff (GER) bt Marin Cilic (CRO x9) 6-2, 6-3
Kei Nishikori (JPN x6) bt Taylor Fritz (USA) 6-2, 6-4
Stefanos Tsitsipas (GRE x8) bt Jannik Sinner (ITA) 6-3, 6-2
Fabio Fognini (ITA x10) bt Radu Albot (MDA) 7-6 (8/6), 6-3
Roger Federer (SUI x3) bt Joao Sousa (POR) 6-4, 6-3
Fernando Verdasco (ESP) bt Dominic Thiem (AUT x5) 4-6, 6-4, 7-5
Rafael Nadal (ESP x2) bt Jeremy Chardy (FRA) 6-0, 6-1
Diego Schwartzman (ARG) bt Matteo Berrettini (ITA) 6-3, 6-4
Fernando Verdasco (ESP) bt Karen Khachanov (RUS x11) 7-5, 3-6, 6-3
Naomi Osaka (JPN x1) bt Dominika Cibulkova (SVK) 6-3, 6-3
Mihaela Buzarnescu (ROU) bt Julia Goerges (GER x16) 6-4, 3-6, 4-4 retired
Carla Suarez Navarro (ESP) bt Alize Cornet (FRA) 6-3, 3-0 retired
Kiki Bertens (NED x6) bt Amanda Anisimova (USA) 6-2, 4-6, 7-5
Marketa Vondrousova (CZE) bt Simona Halep (ROU x3) 2-6, 7-5, 6-3
Daria Kasatkina (RUS) bt Katerina Siniakova (CZE) 2-6, 6-4, 6-1
Johanna Konta (GBR) bt Sloane Stephens (USA x7) 6-7 (3/7), 6-4, 6-1
Garbine Muguruza (ESP) bt Danielle Collins (USA) 6-4, 4-6, 6-2
Sofia Kenin (USA) bt Madison Keys (USA x13) 6-7 (2/7), 6-3, 6-4
Kristina Mladenovic (FRA) bt Belinda Bencic (SUI) 6-2, 2-6, 6-1
Maria Sakkari (GRE) bt Anett Kontaveit (EST x14) 6-3, 6-2
Petra Kvitova (CZE x2) bt Yulia Putintseva (KAZ) 6-0, 6-1
Naomi Osaka (JPN x1) bt Mihaela Buzarnescu (ROU) 6-3, 6-3
Kiki Bertens (NED x6) bt Carla Suarez Navarro (ESP) 6-4, 1-6, 6-3
Johanna Konta (GBR) bt Venus Williams (USA) 6-2, 6-4
Victoria Azarenka (BLR) bt Garbine Muguruza (ESP) 6-4, 3-1 retired
Kristina Mladenovic (FRA) bt Ashleigh Barty (AUS x8) 6-2, 6-3