Reigning Olympic champion Alexander Zverev saved two match points in a remarkable comeback to win his singles tie in an epic three-setter and then helped clinch the United Cup final for Germany in the deciding mixed doubles match on Sunday. (More Tennis News)

The sixth-ranked Zverev showed plenty of stamina in returning from the previous night's early morning finish to rally from a set down and two match points and defeat the No. 9-ranked Hubert?Hurkacz 6-7 (3-7), 7-6 (8-6), 6-4 in a three-hour epic at Ken Rosewall Arena in Sydney.?

Then, playing his sixth match in three days, including a 2.20 AM local time finish on Sunday in Germany's marathon semifinal victory over Australia, Zverev partnered with Laura Siegemund to win the mixed doubles 6-4, 5-7, 10-4 in a super tiebreaker against Iga Swiatek and Hurkacz.

Fittingly, the winning shot was off Zverev's racquet as his backhand volley winner clinched for Germany what had appeared an unlikely United Cup title after nail-biting victories in the semifinal and in Sunday's final.

Earlier, top-ranked woman Swiatek had given Poland an early lead with a straight-sets win against Angelique Kerber.

The 22-year-old Swiatek beat Kerber 6-3, 6-0 in 70 minutes to stretch her win streak to 16 matches, after the four-time major winner finished 2023 with title wins at the China Open and the WTA Finals in Mexico.

Swiatek's victory meant Poland needed just one more win from the remaining men's singles or mixed doubles match to claim the United Cup.?

Hurkacz appeared to have Poland well on the way to its maiden team title as he led Zverev by a set and 6-4 in the second set tie-breaker.? Somehow, Zverev found the energy and a superb running cross-court forehand that clipped the line to keep Germany in the tie.

He then served out the second set to level the match and clinched the deciding set with a break in the third game to close out a thrilling contest in just under three hours.

“I mean, also I saved a match for hitting a passing shot this much on the line," Zverev said. "So, this is how tennis goes sometimes. You win and lose by millimetres sometimes.

Earlier, Kerber, who saved two match points against Australia's Ajla Tomljanovic in the semifinal on the way to her first singles win since returning from the birth of her first child, provided a stern test for Swiatek in a tight opening set.?

The former top-ranked player had break-point opportunities on Swiatek's serve in the fourth and sixth games but could not convert as the Polish player scrambled through to hold.?

The 22-year-old Swiatek took her opportunity to seize the advantage in the seventh game and clinched the set in 48 minutes.

Swiatek stepped up a gear in the second as she broke the three-time major winner three times to close out her fifth consecutive win this week and leave Poland just one win away from a maiden team event title.?

“I'm really proud of myself that I could win all my singles,” Swiatek said post-match. ”(Kerber) was really picking the right spot to play and she surprised me sometimes at the beginning of the set with her decision-making and choices.

“I knew that she could play like that, but I didn't have much time to get into the rhythm because she was really aiming for, sometimes, these balls inside-out, and it was pretty hard."