WATCH the Hamburg Open LIVE in Australia on beIN SPORTS | Subscribe here and take advantage of our 7-day FREE TRIAL

Paul delivered a resilient performance on the clay to defeat the world No.9 2-6 6-3 6-3 in two-hours and 16 minutes.

After saving two break points in the opening game of the match, De Minaur converted two of a possible four break points to clinch the first set.

The Australian carried his momentum into the second, racing into a 3-0 lead as Paul found himself in trouble in Germany.

However, the No.6 seed reeled off six consecutive games, giving away just five points in his three service games to force a decider.

Tthere was no turning back from Paul, whose one converted break point was enough to seal victory, which he did with his third match point.

It was a huge disappointment for De Minaur, who appeared to have put his recent woes on clay behind him with stirring wins over Luciano Darderi and Cameron Norrie on his way to the last four in Germany.

But defeat to Paul adds to a list of losses to lower-ranked opponents, having also lost to Rafael Jodar and Valentin Vacherot leading into Hamburg.

It was only Paul's second win over De inaur in seven meetings, and after the first set, it looked as if he was on his way to another defeat.

"I was in panic mode, down a set and 3-0," Paul said.

"I thought he was playing amazing tennis and I was just trying to find ways to win points. I feel like I stayed resilient, put balls in, made points longer and I started finding my forehand. I shifted it and started playing some really good tennis."

In the other semi-final, world No.57 Ignacio Buse needed just 64 minutes to dispatch American Aleksandar Kovacevic 6-1 6-4.

Elsewhere in Geneva, Mariano Navone stunned No.6 seed Casper Ruud 7-5 6-2 to reach the final.

On the other side of the draw, Learner Tien overcame Alexander Bublik in a tough battle, winning 6-1 4-6 7-6 (7-5).