India's Rohan Bopanna has crashed out of the singles event of the ATP Challenger tournament in Aachen, Germany.Bopanna, who had entered the singles main draw as a qualifier, lost his opening round match 2-6 5-7 to local lad Simon Stadler.However, he and his Pakistani partner Aisam-ul-Haq Qureshi, seeded second, booked a quarterfinal berth in the doubles event with a 7-5 6-2 win over Croat Wild Card pair of Nikola Mektic and Ivan Zovko.