Bublik, who regularly delivered first serves at speeds of more than 220 km per hour, gave his opponent no chance on his own serve to make his first final of the year as the grass season heads towards Wimbledon in just over a week.

Zverev, a two-time finalist in Halle, quickly dropped a break behind with Bublik racing to a 4-1 lead in the first set.

The German's return was no match for the Kazakh's thundering serve and Bublik quickly wrapped up the first set in 35 minutes.

Bublik, who reached his second tour semi-final of the season after Italian Jannik Sinner was forced to retire injured, had two more break chances at 3-3 but Zverev dug deep to stay in the contest.

However, the Kazakh played a flawless game at 5-5 to snatch the break he wanted with a superb crosscourt forehand winner and then served out the match.

The world number 48 will face Andrey Rublev in Sunday's final after the Russian beat Roberto Bautista 6-3, 6-4.

If Rublev lifts his 14th tour-level trophy, he will have captured an ATP 500 title on grass, clay and hard courts.