Fifth seed Aryan Goveas, who won the ITF junior event at Delhi last week, and third seed Vasisht Cheruku were the other Indians to make the last four grade in boys' section at the Mhalunge Balewadi Tennis Stadium.
On the other hand, Vasanti Shinde of Pune and Mihika Yadav made it to the last four in the girls' event.
Under-14 national champion Banthia, a student of the Bishops School who has gained a wild card, took two and a half hours to topple the 16-year-old Briton 6-4, 2-6, 6-3. He will next take on Goveas, who overcame a inflamed eye and a fighting Nick Consalvo of Australia to win 3-4, 6-4, 6-2 in another quarter-final match.
In the girls' event, fourth seed Vasanti overcame a first set loss against fifth seed Georgina Axon of Britian and recorded a hard-fought 2-6, 6-3, 6-2 win.
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She will take on top seed Tamachan Momkoonthod of Thailand, who disposed off sixth seed Zeel Desai 6-2, 6-3 to enter the last four.
Third seed Mihika of Mumbai scored a convincing 6-3, 6-3 win to oust Taipei's Huang Hsiang Wen and will clash next with second seeded Plobrung Plipuch, who stopped the run of Sama Sathwika 6-4, 6-4.
Boys singles (Quarterfinals): Jay Clarke (GBR,1) bt Paramveer Singh Bajwa (Ind,6) 7-5 6-2; Vasisht Cheruku(Ind,3) bt Rian Pandole (Ind) 6-2 6-0; Siddhant Banthia(Ind) bt Jack Macfarlane (GBR,4) 6-4 2-6 6-3; Aryan Goveas (Ind,5) bt Nick Consalvo (AUS) 3-4 6-4 6-2.
Girls singles (Quarterfinals): Tamachan Momkoonthod (THA,1) bt Zeel Desai(Ind,6) 6-2 6-3; Mihika Yadav (Ind,3) bt Huang Hsiang Wen (TPE,7) 6-3 6-3; Vasanti Shinde (Ind,4) bt Georgina Axon (GBR,5) 2-6 6-3 6-2; Plobrung Plipuch (THA,2) bt Sama Sathwika (Ind) 6-4 6-4.