Austrian world number eight Dominic Thiem was full of praise for Alex de Minaur after being given a fright by the Australian teenager in their Davis Cup reverse singles rubber.

Thiem beat the 19-year-old 6-4, 6-2, 3-6, 6-4 in an absorbing match that lasted almost three hours on outdoor clay at the Messe Congress complex in Graz on Sunday.

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The 25-year-old French Open finalist, who also ended Rafael Nadal's 51-week unbeaten run on clay at the Madrid Open in May, delivered his nation an unassailable 3-1 lead to ensure they'll be seeded in February's qualifying round for the new-look competition.

Despite the defeat, de Minaur's performance against one of the best players in the world on home soil and on his favoured surface is another positive sign in what's been a magnificent 12 months for the world number 38 from Sydney.

"Alex has proved he's world class this year," Thiem said.

"At the US Open he played really good which was on a pretty slow hard court so I was not that surprised by how well he played today."

Having raced into a two-set lead, Thiem looked on course to wrap up a routine victory similar to his dismantling of Jordan Thompson in Friday's opening rubber.

But the resilient de Minaur took out the third set and then had two glorious opportunities to force the match to a decider after twice breaking Thiem's serve.

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However, the Austrian broke back immediately on both occasions then saved his third break point of the set before holding his nerve to close out the win.

"I think I was really close," de Minaur said.

"Being up a break in the fourth, I played not my greatest game and then I still had another break point at 4-4 so I really thought I was points away from going to the fifth and then anything could have happened.

"At the end of the day, I've just got to learn from these things.

"They do sting a lot but it's a learning process for me and hopefully next time I'm in the same situation I don't make the same mistake."

Australian captain Lleyton Hewitt said he was proud of how his undermanned team performed in the absence of Nick Kyrgios.

"We came here to win, but we also came here to give 100 per cent and leave it all out here, and if we weren't good enough, we weren't good enough," Hewitt said.

"But I couldn't be prouder of my team — the guys that played, the guys that didn't play.

"Everyone came here, they prepared, they did absolutely everything that we asked them to and they left it all out there."

AAP