Zverev, in strong form, claimed the first set against Blockx comfortably but struggled to break the Belgian in the second, before eventually finding a way through.
"I'm very happy of course to be in a final," said Zverev, who lifted the trophy in Madrid in 2018 and 2021.
"There were a lot of tough matches, a lot of tough battles... and I'm looking forward to playing Jannik again.
"Tennis is very very easy for him right now, the way he is playing. Maybe on Sunday I will make it a bit more difficult for him.
"He's the best player in the world for sure, and I'm just trying to give him a tough battle."
The 29-year-old broke in the first and fifth games to surge into a 5-1 lead against his unseeded opponent.
Underdog Blockx, ranked 69th in the world, resisted strong pressure on his next service game, saving three set points to hold.
However, the dominant Zverev made no mistake with his fourth chance to wrap up the fourth stanza, laying down an ace.
Blockx survived two break points in the first game of the second set and another in the third as Zverev worked him hard.
The Belgian, who defeated Casper Ruud in the quarter-finals, put up a brave display as he saved two more break points in each of the seventh and ninth games.
Eventually, Zverev took his eighth break point of the second set to nose 6-5 ahead, with a fortuitous net cord that broke Blockx's resistance.
The German, who has suffered a string of semi-final defeats this season, made it to his first final with a powerful overhead winner.
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