Who was the first european to discover the pacific ocean by crossing the isthmus of panama?

According to historical sources, the first European to discover the Pacific Ocean was Vasco Nuñex de Balboa. This ocurred on the 25th of September 1513, almost a month after he departed from Santa Maria La Antigua del Darién.

Explanation:

Balboa embarked in this expedition to assert his power over the Spanish Colony near the gulf of Uraba, and to use the supposed riches of the new sea to hold his defense against his enemies that had sent envoys to the Spanish Court of Charles V.