Seeded eighth, the Indo-Vietnamese duo defeated fifth seeds Miomir Kecmanovic of Serbia and Casper Ruud of Norway 7-6 3-6 12-10 in the last-four match that lasted two hours and 20 minutes on court number three.
Earlier, they had beaten Japanese combination of Yusuke Takahashi and Jumpei Yamasaki 6-2 6-3 on grass Court No.6 of the All England Club to reach the semifinals.
The 17-year-old Delhi-born Nagal and his partner will take on American-Japanese fourth seeds Reilly Opelka and Akira Santillan in the title clash.