Greece's Stefanos Tsitsipas may be the star attraction at the Next Gen ATP Finals but Australian Alex de Minaur said Thursday he was "having a hell of a year" as both raced into the semi-finals of the season-ending tournament for players aged under-21 with only one set dropped in three games.

Tsitsipas, ranked 15th in the world, will take on last year's finalist Andrey Rublev in Friday's semi-finals with de Minaur, 19, up against Spaniard Jaume Munar.

"I'm playing well, I'm feeling well, and I'm happy to be the star," said Tsitsipas, 20.

"But I know there's another star who had three wins in a row in the other part of the draw. So the tournament is not over yet."

The Greek player, in Group A in the round robin tournament, was referring to de Minaur who also won his three matches in Group B.

The Australian began the season at number 208 and reached a career-high 31 last month.

"It's definitely a big surprise. I never expected almost anything that happened this year," said the player from Sydney.

"It's been a hell of a year. I've enjoyed every second of it and it's given me a hunger for more."

De Minaur beat American Taylor Fritz 4-3 (10/8), 4-1, 4-2 on Thursday with Tsitsipas racing past Poland's Hubert Hurkacz 4-1, 4-3 (7/2), 4-1

Rublev eased past Italian wild card Liam Caruana 4-3 (9/7), 4-1, 4-2 to book his passage after losing to de Minaur on Wednesday, with Munar beating American Frances Tiafoe 4-1, 4-3 (7/3), 4-1 to seal the final berth.

The format for the tournament is the best-of-five sets with shorter sets of four games, no-ad scoring at deuce and no lets on serve.