Osaka beats Mertens, braves heat to reach first 2026 quarterfinal in Bad Homburg

Naomi Osaka is into her first quarterfinal of the season Tuesday, defeating Elise Mertens 6-3, 6-3 in 67 minutes in Bad Homburg. It also marks her first grass-court quarterfinal since 's-Hertogenbosch in 2024.

Bad Homburg: Scores | Order of play | Draws

Osaka also beat Mertens en route to the last eight at that event. The four-time Grand Slam champion is now 2-0 against Mertens on grass and leads their WTA Tour Driven by Mercedes-Benz head-to-head 5-3.

Osaka raced to a 5-0 lead in the opening set before Mertens closed the gap to 5-3, echoing Osaka's first-round match against Magdalena Frech, when a 5-0 lead shrank to 5-4. In that match, Mother Nature helped her reset. This time, Osaka said a steadier mindset made the difference.

"In my last match I had a huge dip in the first set, and this time I tried to be pretty stable," Osaka said in her on-court interview. "So it's honestly really fun to learn match by match."

She closed out the first set in 31 minutes on her second attempt to serve it out, then took full control of the match. Osaka broke first in the second set and never looked back.

Here were the keys to victory for the former World No. 1.

Serving dominance: Aside from the late first-set break, Osaka was virtually untouchable on serve. She hit seven aces and won more than 86% of her first-serve points, dropping just four (25 of 29). She also held a 12-point edge in second-serve points won, 47% to 35%.

Her serve grounded her through the tight moments late in the first set and carried her through the second. After breaking for 2-1, she held for 4-2 with a pair of aces and held to love for 5-3 before closing out the match with a break to love.

Consistent groundstrokes: Osaka backed up her serve with quality hitting. She finished with 22 winners to just eight unforced errors and dictated play with her forehand, which accounted for 11 winners. She changed direction with ease and kept Mertens off balance and on the defensive throughout.

Her final forehand winner came on the penultimate point; the seventh of eight straight points she won to finish the match.

Beating the heat: As if contending with Mertens wasn't enough, Osaka also had to handle the conditions, with temperatures reaching 90 degrees Fahrenheit Tuesday.

But the heat never bothered her anyway.

"I'm pretty heat-tolerant," Osaka said afterward. "I really love the heat. I kind of prefer it. It was hot in Paris a few weeks ago and I also enjoyed that, so I kind of want it to be hot."

The forecast should continue to favor her. With temperatures expected to reach 93 degrees Thursday, the No. 6 seed will face the winner of Roland Garros champion Mirra Andreeva and Ekaterina Alexandrova for a spot in the semifinals.