Prakash and his American Brendan Evans had to dig deep to beat Mikhail Kukushkin of Kazakhstan and Alessandro Motti of Italy as they carved out a hard fought 6-4 4-6 10-5 in the opening round of the euro 425,000 event.
Mankad and his Jamaican partner Dustin Brown also fought hard after a first-set lapse but eventually lost 1-6 7-6(4) 7-10 to second seeded British pair of Jonathan Marray and Jamie Murray.
Amritraj and Evans have a tough next round as they are up against third seeds Daniele Bracciali of Italy and Jonathan Erlich of Israel.
Amritraj had exited from the singles competition after losing to local wild card Marco Crugnola in the first round.