The 48th-ranked Bublik hit 14 aces and saved the only break point he faced from 22nd-ranked Zverev.
“The job is not finished, there is one last match,” the Kazakh player said. “I am happy but I try to stay focused.”
Zverev reached the Halle final in 2016 and 2017. He was aiming for his first title since 2021.
Bublik is looking for his second career trophy after winning in Montpellier last year, while Rublev will be looking for his second of the season after triumphing in Monte Carlo in April. The seventh-ranked Russian seeks his 14th title altogether and his first on grass.
Alexander Bublik to face Andrey Rublev in Halle Open final