Ramkumar, who had also shocked Somdev at the Chennai open early this year, overcame the challenge of sixth seed Yuki 7-6 (4) 6-3 to move to the quarterfinals of the USD 50,000 hard court tournament.
The 19-year-old Chennai youngster has been impressive this year, having won four ITF Futures singles title so far.
There was no break of serve in the opening set but Ramkumar succeeded in breaking his senior compatriot twice in the second set of the match, which lasted one hour and 45 minutes.
Now only three Indians are left in the singles main draw, Ramkumar, Saketh Myneni and Sanam Singh.
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Ramkumar will take on Chinese Taipei's Ti Chen, who overcame Frenchman Fabrice Martin 6-7(5) 6-4 6-4. Saketh and Sanam will clash against each other.
Later in the day, Yuki and Divij Sharan, seeded second, moved to the semifinals with a 7-6(4) 6-2 win over Japanese pair of Hiroki Moriya and Yasutaka Uchiyama.