Prannoy recovered from a game down to outwit sixth seed Christie 18-21, 21-16, 23-21 in a thrilling contest that clocked an hour and 15 minutes.
It was Saina's fourth straight loss to world No. 12 Busanan.
Parupalli Kashyap exited from the tournament after he retired in the third game of his first-round clash against Canada's Jason Anthony Ho-Shue owing to a calf injury.
Srikanth lost to second seed Chou Tien Chen of Chinese Taipei 22-20, 13-21, 16-21.
Srikanth, seeded fifth, defeated Ho-Shue 21-15, 21-14 in just 33 minutes to make it to the last eight of the Super 750 tournament.
'With so much time available and nothing much to do, I have been sleeping mostly,' says the former world No. 1.
The positives for India were reigning world champion P V Sindhu and youngster Lakshya Sen who progressed to the second round.
London Olympics bronze medallist Saina Nehwal secured a straight game win over Ukraine's Maria Ulitina to storm into the women's singles quarterfinals.
India finished second in the group and will take on Thailand in the quarterfinals on Friday.
Kidambi Srikanth spearheaded India's 4-1 thrashing of Kazakhstan in their opening group match.