On day one of the knockout segment of the competition, Shagun, 16, stunned Tvesa, who last year even won a pro tournament whilst still being an amateur.
The match went to the wire before Shagun emerged winner.
Shagun will now meet Sifat Alag, who beat Tanirika Singh 2&1.
Favourite and topper in the stroke play segment, Malaysia's Nur Durriah Damian was taken the full distance by 17-year-old girl from Punjab, Gurjot Badwal.
Nur, the three-time Malaysian Amateur champion, finally won 1-up after 18 holes. She will now meet Pranavi Urs, who beat Nur Maisara Saad 5&4.
Seher will have tough second round against local Sifat Sagoo, the talented 15-year-old who beat another Malaysian Liyana Durisic 3&2.
The day's biggest win was achieved by Singaporean Amanda Tan, who defeated Bangladesh golfer Jakia Sultana 7&6 as the match ended on the 12th green.
India's top draw Diksha Dagar, who beat Shuraz Singh 6&4, will meet the in-form Singaporean Amanda next.
Results: Matchplay Round 1 (all players Indian unless otherwise mentioned): Nur Durriah Damian (Mas) bt Gurjot Badwal 1-Up; Pranavi Urs bt Nur Maisara Saad (Mas) 5&4; Seher Atwal bt Gemma Clews (Eng) 6&5; Sifat Sagoo bt Liyana Durisic (Mas) 3&2; Gauri Karhade bt Ananya Barthakur 2&1; Zethu Myeki (SAF) bt Noramal Nuchsila (Tha) 3&2; Maria Dunne (Ire) bt Siripatsorn Patchana (Tha) 2-Up; Geraldine Wong (Mas) bt Liza Akhter Bangladesh) 2-Up; Shagun Narain bt Tvesa Malik 1-Up; Sifat Alag bt Tanirika Singh 2&1; Amanda Tan (Sin) bt Jakia Sultana (Bangladesh) 7&6; Diksha Dagar bt Shiraz Singh 6&4; Tsai Wei Chia 9 Taipei) bt Yavnika Duhan 3&2; Dolma Rawat bt Arshia Mahant 2&1; Callista Chen (Sin) bt Trimann Saluja 4&3; Anika Varma bt Seerat Kaur Alag 4&3.
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