De Minaur's Next Gen final heartbreak

Missed break-point opportunities proved decisive for Alex de Minaur against Jannik Sinner

Alex de Minaur has only lost two of his 10 matches in two editions of the Next Gen ATP Finals but unfortunately for the Australian No.1 they were both finals.

On Saturday, the top seed was unable to capitalise on a stack of break-point chances as Italian teenager Jannik Sinner stormed to victory to secure his maiden ATP title.

Tournament wildcard Sinner thumped winners with incredible regularity off both wings and overpowered world No.18 de Minaur 4-2 4-1 4-2 in one hour and four minutes, to the delight of the crowd in Milan.

For the second consecutive year de Minaur rolled into the decider with a perfect 4-0 record at the season-ending tournament for top under-21 players.

But again the 20-year-old will have to be content with a runner-up finish - and $295,000 ($A430,000) in prize money - after losing to Stefanos Tsitsipas 12 months ago.

De Minaur said the match against Sinner was one of missed opportunities.

"It's a pretty simple match to evaluate," he said.

"I had nine break points and I wasn't able to convert any of them.

"Jannik played a really impressive match. He was putting me under pressure.

"In the end he just played too good."

Sinner came up with answers when required against de Minaur as the 18-year-old recorded the biggest win of his career.

"He's an unbelievable player," Sinner said of de Minaur.

"I just tried to play my game and not make any errors.

"I didn't make many so I'm very happy with my performance."

The youngest player in the field this week, Sinner picked up $372,000 ($A542,000) from this week's tournament, surpassing his career total before arriving in Milan.

But he doesn't plan on splashing out to celebrate.

"No," Sinner said with a smile when asked if he was going to buy himself something special.

"Sinner-Mania" is sure to grow. His run in Milan has stirred the crowds this week to near-hysteria.

The title capped a fantastic season for the 18-year-old Sinner who opened the year at world No.551 but is now the youngest player inside the Top 100, having risen to 95th.

He only recorded his first ATP Tour main-draw win in April.

In a good omen for Sinner, both Tsitsipas and inaugural Next Gen winner Chung Hyeon reached the Australian Open semi-finals two months after capturing their titles.