BIRMINGHAM, Great Britain -- Slovenian qualifier Dalila Jakupovic picked up her second Top 20 win in a row at the Nature Valley Classic, advancing to the quarterfinals on Wednesday after World No.18 Naomi Osaka was forced to retire due to injury while Jakupovic led 6-3.

"It’s never nice to win when somebody’s injured," Jakupovic said during her on-court, post-match interview. "I was trying to focus on my play, and I didn’t really look on her side. I hope [Osaka's] going to be better for the next tournaments."

Before the retirement, Jakupovic matched Indian Wells champion Osaka power for power, with 11 winners to the Japanese star's nine, and seven unforced errors for each. The Slovene also converted both of her break chances, while the hampered Osaka was 0-for-3.

"I'm powerful too!" Jakupovic exclaimed with a laugh, on court. She also said that her run through qualifying and her long comeback win over World No.17 Elise Mertens in the first round "didn’t help me a lot, I’m very tired! It was a long week, so I’m happy to have a day off tomorrow." Jakupovic's win over Mertens was the first Top 20 victory of her career.

Jakupovic will face another Top 20 player, Slovakia's Magdalena Rybarikova, in the final eight in Birmingham. World No.19 Rybarikova, a semifinalist at Wimbledon last year, overcame former Top 10 player Kristina Mladenovic, 3-6, 6-2, 6-1, earlier on Wednesday.

Both Jakupovic and Osaka were using their aggressive games, complete with flat, hard groundstrokes, to attempt to take early command of the set. Osaka held for 1-0 with an ace on game point, and Jakupovic leveled at 1-1 with a game-ending ace of her own.

The Japanese player then held for 2-1 with a forehand winner, and dragged the following game to break point after a Jakupovic double fault, hoping to get a 3-1 lead. But the Slovene erased that chance with a well-timed backhand winner, and held for 2-2.

Energized by that escape, Jakupovic continued to play a risky, powerful game that worked to great effect and frustrated Osaka in the process. At 3-3, the Slovene opened the game with a searing backhand service return winner, at which Osaka could only smile in amazement. Another backhand winner allowed Jakupovic to break Osaka at love for a 4-3 lead.

Osaka fought back in the following game, blasting a forehand volley to reach break point. That chance was lost, and a second break point was also not converted. Jakupovic eventually pulled through the game to hold for 5-3, forcing Osaka to serve to stay in the opening set.

In that game, Osaka quickly fell behind 15-40, giving Jakupovic double set point. Once again, Jakupovic’s backhand paid dividends, with a winner off of that wing to break and seal a one-set lead. Afterwards, Osaka had a brief visit from the trainer, and the Japanese youngster determined that she was too afflicted to start the second set, sending Jakupovic into her maiden WTA Premier-level quarterfinal.