Third seed Somdev, who is enduring a tough season, lost 3-6 6-7(3) to Czech Adam Pavlasek in one hour and 35 minutes for his second successive second-round defeat in the home Challenger events.
27-year-old Myneni, winner of last week's Indore Open, knocked out fifth seed and higher-ranked seed Japanese Hiroki Moriya 6-1 6-2 in just 55 minutes.
In a repeat of last week's final, Myneni will now fight it out with top seed Kazak Aleksandr Nedovysov.
However, in the bottom-half of the draw, it was end of road for Sanam Singh, national hard-courts champion Vishnu Vardhan and qualifier Vijay Sundar Prashanth.
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Sanam was outplayed 1-6 2-6 by Adrian Menendez-Maceiras while Vardhan went down fighting 2-6 6-3 3-6 against eighth seed Kimmer Coppejans, also from Spain.
Prashant was ousted 0-6 6-7(5) by second seed Alexander Kudryavtsev.
In the doubles, Somdev and Prashanth pulled off an upset win over top-seeded Thai pair of Sanchai and Sonchat Ratiwatana 6-7(4) 3-6 to move to the semifinals.