Alexander Zverev won both his singles and mixed doubles matches against Greece on Friday to lead Germany into the United Cup semifinals against Australia.
Zverev and Laura Siegemund beat Maria Sakkari and Petros Tsitsipas 6-3, 6-3 in the deciding mixed doubles to clinch Germany's 2-1 victory after Zverev beat Stefanos Tsitsipas 6-4, 6-4 in singles. Sakkari beat former Australian Open champion Angelique Kerber 6-0, 6-3 to give Greece the early lead.
France will play Poland in the other semifinal match Saturday. The final is set for Sunday, at Sydney's Ken Rosewall Arena.
Sakkari had lost three of her four previous career meetings with Kerber. But those defeats came before her rise to the world's top 10 and the 35-year-old Kerber's break to have a child.
"I was just very solid from the baseline, doing what I have to do," Sakkari said. "But of course I knew that Angie, because she's very experienced, an amazing player, that she was going to find a way to come back. I managed my nerves really well, especially in that second set."
Zverev is unbeaten in the season-opening mixed teams event.
"I had to come out aggressive. I knew that," No. 7-ranked Zverev said of his game plan to beat Tsitsipas for the fifth time in 14 matches, adding, "He is one of the best, maybe the best aggressive players in the game. If he's on the front foot, it's extremely difficult to play against him.
"That's why I have a not-so-good record against him because he is somebody that is difficult for me. But Germany and I needed that win, and I'm happy about that."
Zverev, who lost in the second round of last year's Australian Open following his comeback from an ankle injury, is hoping to progress further in the Grand Slam this year.
"Being healthy is the biggest thing for any athlete. The mindset this year is different," Zverev said. "I hope that I can stay in Australia a bit longer, maybe a bit more successful. I've already won more matches this year than I did last year, so I'm happy."
The Associated Press and Reuters contributed to this report.