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.

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 job is not finished, there is one last match," Bublik said. "I am happy but I try to stay focused. I tried to play my game and I am really happy with the win today. Playing Sasha is really tough and I was a bit lucky in the key moments."

The world number 48 will now play third seed Andrey Rublev who found little resistance from Roberto Bautista-Agut, who has not reached a final on grass in nine years.

The Russian's precision left the Spaniard stunned at times and he was broken only once in the match as he reached the final where he will bid to win his second title of the season.