Two-time champions Croatia reached the Davis Cup Finals on Sunday where they were joined by unheralded South Korea and Finland.

Croatia, the champions in 2005 and 2018, were 2-0 up on Austria in their qualifier in Rijeka overnight.

Lucas Miedler and Alexander Erler then upset doubles specialists Nikola Mektic and Ivan Dodig 6-3, 7-6 (13/11) to keep Austria in the tie.

However, world number 23 Borna Coric won his second singles rubber, seeing off former US Open champion Dominic Thiem 7-6 (7/3), 6-2 as Croatia joined the 16-nation group stage of the finals in September.

"I was pretty nervous," said Coric. "But I came out on court and I was playing great tennis today."

In arguably the performance of the qualifying round, South Korea overturned a 2-0 deficit to beat Belgium 3-2 in Seoul.

Hong Seong-chan, ranked 237 in the world, clinched the deciding point with a 6-3, 7-6 (7/4) win over Zizou Bergs, ranked 122 places higher.

"The players made history as a team. It's a dream to advance to the finals for two consecutive years," said South Korea captain Park Seung-kyu.

Nam Ji-sung and Song Ming-kyu started the South Korean fightback with a 7-6 (7/3), 7-6 (7/5) doubles win against Sander Gille and Joran Vliegen.

Kwon Soon-woo then stunned David Goffin 3-6, 6-1, 6-3 on the back of 11 aces to level the tie.

"We had opportunities in every match but time after time we didn't succeed," said Belgium captain Johan van Herck.

Finland made the finals stage for the first time with a 3-1 win over 2016 champions Argentina in Espoo.

Emil Ruusuvuori won all three rubbers he played.

On Sunday, he teamed with Harri Heliovaara for a 7-6 (7/5), 4-6, 6-4 win over Maximo Gonzalez and Andres Molteni.

The 23-year-old then fittingly secured the winning point by seeing off Facundo Bagnis 7-5, 6-1.

"It's an incredible feeling to play this kind of tennis in front of the home crowd," said world number 43 Ruusuvuori.

Three-time winners Czech Republic beat Portugal with impressive 21-year-old Jiri Lehecka sealing victory with his second singles success of the weekend, a 6-4, 6-1 triumph over veteran Joao Sousa in Maia.

The Netherlands defeated Slovakia in Groningen with Tallon Griekspoor and Tim van Rijthoven seeing off Alex Molcan and Lukas Klein 6-3, 6-3.

Chile downed Kazakhstan 3-1 at home to also make the last 16.

On Saturday, 37-year-old Stan Wawrinka, making his first appearance in the Davis Cup since 2015, won the deciding rubber as Switzerland defeated Germany.

Also making it through were 10-time winners France, Serbia, Britain, Sweden and the United States.

The weekend's 12 winners all go through to the group finals in September where they will be joined by 2022 champions Canada, runners-up Australia and wild cards Spain and Italy.

The top eight then progress to the Davis Cup Finals knockout week in Malaga in November.

Meanwhile, in the World Group One play-offs, world number three Stefanos Tsitsipas, the highest-ranked player in action this weekend, helped Greece to victory over Ecuador.

Australian Open runner-up Tsitsipas won both his singles rubbers to the delight of 12,000 fans at the Athens Olympic Centre.

"We want to play here in a Davis Cup final. I believe if that happens, it will be unforgettable," said Tsitsipas.

Fellow top-10 star Holger Rune was also a two-time winner, helping Denmark defeat India at Hillerod.