Getting the title of Vedānta Deshikan and Brahma Tantra Swatantra

Once a band of Maayaa Vaadhis landed in Shrīraṅgam for a debate condemning Rāmānuja Darsanam. Periya Vaachaan Pillai, Pillai Lokaachaarya, and others resorted to the Grand old Master Sudarsana Bhattar for advice. Sudarsana Bhattar said that only Swami Desika could save the situation, and a letter was sent to Kanchi inviting Thooppul Pillai to face the opponents. Swami immediately set forth for Shrīraṅgam, but on the way, he halted at Sriperumbudur and prayed to Yathirajar, composing the famous Yathiraja Saptadhi.

On reaching Shrīraṅgam, Swami fell at the feet of Sudarsana Bhattar and sought his blessings. Bhattar blessed him, saying that the Perumals (Sri Rangam Ranganathar, Tirumala Srinivasar, and Kanchipuram Varadar) commanded that he should re-establish our Siddhanta as Rāmānuja had earlier. The debate lasted for seven days, during which Swami demolished every single argument of the opponents. The Maayaa Vaadhis accepted defeat, became Srivaishṇavas and his Sishyas.

The essence of the debate is what we now have as "Satha Dushani".It was at this time that Periya Perumāl conferred the title "Vedānta Deshikan" and Periya Piraatti the title "Sarva Tantra Svatantra." Sudarsana Bhattar and Periya Vaachaan Pillai commended on this and declared that he was the one who deserved the honorific most eminently.