Fourth Seed Saina took just 31 minutes to dispose off Petya 21-18 21-9 and will take on the winner of eighth seed Tine Baun and Japan's Ayane Kurihara in the quarterfinal tomorrow.
In the first game, Saina opened up a four-point lead at 6-2 and though the Bulgarian caught up with her at 12-all, the Indian was successful in keeping her nose ahead to pocket it after a close-fight.
The 21-year-old Indian turned more aggressive in the second game and after leading 5-2 kept taking giant strides forward to widen the gap and eventually took the game away from Petya.
Saina won the Indonesian Open twice on consecutive years in 2009 and 2010.
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