Madrid - Naomi Oaska admitted she "was thinking about too many things" in her 3-6, 6-2, 7-5 Madrid Open quarter-final loss to Belinda Bencic on Thursday.
World number one Osaka has claimed the last two majors at the US and Australian Opens and will be looking for a third in succession when she travels to Paris for the French Open later this month.
However, she admitted that knowing her top WTA ranking could possibly be in danger after failing to reach the Madrid semi-finals might have played on her mind mid-match on Thursday.
"I was just thinking about too many things. I wanted to win this match so much because she'd beaten me before -- I didn't want to lose twice in a row," said the 21-year-old.
"People have been telling me if I get to the semis here, I can stay number one.
"I wanted to do that but I was thinking about it while I was playing, which wasn't necessarily a good thing."
The Japanese star, who will lose the top ranking if Simona Halep takes the Madrid title, will now head to Rome next week for the final tune-up prior to the May 26 start of Roland Garros.
"I'm really happy as my serve was my biggest concern coming in," she said after losing for the second time in two months to Switzerland's Bencic who also triumphed in Indian Wells.
"I wanted to play this tournament and I'm going to play Rome, too.
"There's a lot of happy things to take from this because I lost in the first round last year so anything is an improvement, honestly."
Bencic, a former top 10 player before injury struck several seasons ago, is now back in the top 20 and determined to lift her standing further.
"Of course I'm very happy," the number 18 said. "I'm in the semi-finals, I beat the world number one and I turned the match around."
She will have a chance to go further on Friday as she plays two-time tournament winner Halep, who booked her last-four-spot with a 7-5, 7-5 win against Australian Ashleigh Barty.
Bencic defeated former number one Halep on her way to the Dubai hardcourt trophy in February.
"It's always long rallies with her. I don't think that's going to change," said Bencic.
"But this is a different surface (than Dubai), a different city, different conditions.
"I'll just have to try to play the same as I always do and focus on my game, focus on myself."
Results from the ATP and WTA tournaments in Madrid on Thursday (x denotes seeding):
Novak Djokovic (SRB x1) bt Jeremy Chardy (FRA) 6-1, 7-6 (7/2)
Marin Cilic (CRO x9) bt Laslo Djere (SRB) 4-6, 6-3, 6-2
Roger Federer (SUI x4) bt Gael Monfils (FRA x15) 6-0, 4-6, 7-6 (7/3)
Dominic Thiem (AUT x5) bt Fabio Fognini (ITA x10) 6-4, 7-5
Stefanos Tsitsipas (GRE x8) bt Fernando Verdasco (ESP) 6-3, 6-4
Stan Wawrinka (SUI) bt Kei Nishikori (JPN x6) 6-3, 7-6 (7/3)
Belinda Bencic (SUI) bt Naomi Osaka (JPN x1) 3-6, 6-2, 7-5
Simona Halep (ROM x3) bt Ashleigh Barty (AUS x9) 7-5, 7-5
Sloane Stephens (USA x8) bt Petra Martic (CRO) 6-4, 6-3