India's Prakash Amritraj has advanced to the singles pre-quarterfinals of the ATP Challenger event in Calabasas in US after his opponent retired mid-way in the first round. Prakash was leading 6-3 3-2 when Serbian Llija Bojoljac opted out of contest. Prakash will now fight it out with third seed Jesse Levine for a place in the quarterfinals. Prakash and his American partner Alex Kuznetsov have already booked a quarterfinal berth in the doubles event.Another Indian in the fray is Harsh Mankad, who has teamed up with Treat Conard Huey of Philippines.