Ramkumar, who had happy memories of upsetting Somdev Devvarman in the previous edition at this venue, suffered a 3-6 3-6 defeat in the first round at the hands of World No. 87 Japanese Tatsuma Ito.
Prasanth was no match to Jiri Vesely of Czech Republic, copping a 2-6 1-6 bashing in 67 minutes.
Playing his aggressive brand of game but without control, Ramkumar hit more winners than his seasoned rival but could not contain unforced errors.
India's singles hopes now rest on struggling Somdev, who is up against formiable Yen-Hsun Lu from Chinese Taipei.
In another first round match, qualifier Aljas Bedene of Slovenia continued with his momentum as he upset world number 94 Lukas Lacko of Slovakia 7-6(7) 6-3 in 97 minutes.
In the pre-quarterfinals, Bedene will take on second seed Feliciano Lopez of Spain.
Earlier in the evening, wild card and 18 year-old Elias Ymer shocked world number 84 Igor Sijsling of the Netherlands 6-4 4-6 6-3 to make it to the second round.
In another singles first round match at the outside court, Ricardas Berankis of Lithuania beat a fighting Italian qualifier Luca Vanni 6-1, 2-6, 7-5 in 108 minutes.
