PERTH, Australia -- Maria Sakkari sealed a Perth City Final place for Greece at the United Cup in Perth with a 6-1, 7-5 defeat of Elise Mertens in 1 hour and 23 minutes.

Greece required only two points from the final tie of Group A to advance, and Sakkari's win backed up compatriot Stefanos Tsitsipas' defeat of David Goffin on the previous day.

Greece will face Croatia on Wednesday night. 

Sakkari and Mertens brought one of the longest-standing rivalries of the competition into this pivotal match. The two 1995-born peers have been squaring off since their days in ITF 10Ks back in 2014, and this was the 10th time they had met in pro action.

Sakkari was broken in the opening game, misjudging a Mertens lob that landed inside the baseline, but shook that slow start off to dominate the first set and a half. She broke back immediately courtesy of a pair of loose Mertens forehands and reeled off 20 of the next 26 points to win a one-sided opener.

Mertens would struggle with her accuracy throughout, racking up 32 unforced errors as well as four ill-timed double faults. Indeed, she trailed 6-1, 3-1 before holding for the first time. Though the WTA No.29 staged a brief fightback, winning three straight games from 4-2 down in the second set, it wasn't enough to deny Sakkari.

The Greek player delivered a watertight performance, committing only 11 unforced errors while remaining aggressive on her backhand side in particular. With the threat of a third set looming, she responded with aplomb to take 12 of the next 13 points to quickly wrap up the match.

"It was a very solid match from my side," Sakkari said. "Obviously I was nervous in the beginning because I knew my match was crucial, but I managed to play a good game, even though in some moments it wasn't pretty. I'm very happy I was able to get us through the group stages."

Things only got better for Team Greece in the fourth match of the tie as Stefanos Sakellaridis upset Zizou Bergs 5-7, 6-1, 6-3 to clinch the tie.

The 18-year-old Sakellaridis is No. 803 in the Pepperstone ATP Rankings, but he shined on his tour-level debut at RAC Arena, where he converted four of seven break points against the physically struggling World No.129 Bergs. The Greek fired eight aces en route to a 2-hour, 13-minute win.

“I don’t know what to say,” Sakellaridis said in his on-court interview. “I came into this match with zero expectation, I just said ‘I’m going to play my match and I’m going to enjoy it.' Obviously, I enjoyed it to the maximum I could, and the win was a bonus, I could never imagine [it].”

Sakellaridis’ win was greeted with joyous celebrations in the Greek Team Zone. Several of the youngster’s teammates ran onto court to lift him up and join in the moment, including Tsitsipas and Sakkari.

In the final match of the tie, Sakkari and Tsitsipas made it a 4-1 victory for Greece by downing Kirsten Flipkens and Michael Geerts 6-3, 6-2 in the mixed doubles. That win improved Greece’s match record for the week to 8-2 as they head into the City Final.