Gulbis, a former French Open semifinalist, will play Stefanos Tsitsipas in Sunday's championship match in his bid for a seventh career title.
The third-seeded Tsitsipas won the first of the semifinals, beating Fabio Fognini 6-3, 6-2. The 20-year-old Greek has yet to win a title.
Gulbis was once ranked No. 10 but is No. 145 after an injury-hit last few years.
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