Sonia (57kg), representing Railways Sports Promotion Board (RSPB) was outwitted 1-2 by Uttarakhand's Kamla Bist, who is also pursuing a coaching diploma from the National Institute of Sports in Patiala.
Sonia's loss was the biggest upset of the tournament, which is largely playing out to expectations. The former Asian silver-medallist delivered a good performance but could not get judges' nod against her equally aggressive rival.
In other results, former World Championships silver-medallist Sarjubala staved off a spirited challenge from Mizoram's Rebecca Lal to enter the quarterfinals.
A tempo boxer, who prefers to go all out from the very first round, Sarjubala was matched punch-for-punch by Rebecca but her failure to sustain the intensity gave Sarjubala the victory.
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The former junior World Championship silver-medallist will be up against Delhi's Pooja Tokas, who outpunched Tamil Nadu's K Nivedita 3-0.
Another former World Championships silver-medallist Saweety Boora (81kg), who is representing Haryana had no trouble sailing past Punjab's Ninderjeet Kaur 3-0.
It was smooth sailing for former junior World Champion Nikhat Zareen (51kg) too. She hardly broke a sweat in her contest against Rajasthan's Jyoti and won comprehensively.
The Telangana girl put up a dominating performance to prevail 3-0 in the contest and set up a clash with Assam's Manju Basumatry. Basumatry got the better of All India Police's Anjali Mehta.
Also making the last-eight stage was former Asian silver-medallist Pavitra (64kg). She scored a Technical Knockout in the third round of her pre-quarterfinal bout against local favourite Nivedita.
Manipur's Sandhya Rani, who had upstaged two-time World Championships bronze-medallist Chhoto Laura in the opening round yesterday, continued her fine form to enter quarters.
She defeated Rajasthan's Neha Bhambu via a Technical Knockout in the third round of her pre-quarterfinal contest.