TRS President and Telangana caretaker Chief Minister K Chandrashekar Rao won from the Gajwel constituency on Tuesday. He won by over 50,000 votes, news agency ANI reported.
The ruling Telangana Rashtra Samiti looks set to sweep the state with wins in two seats and leads in 84 seats so far.
The TRS and BJP contested the polls alone, while the Congress forged an alliance with Telugu Desam Party (TDP), CPI and Telangana Jana Samiti (TJS).
The Assembly was prematurely dissolved on 6 September 2018 with the KCR-led government opting to go for elections more than eight months ahead of schedule.
The state elections were originally scheduled to be held simultaneously with the Lok Sabha polls next year.
In the 119-member Telangana assembly, TRS had 63 seats earlier while Congress and TDP had 21 and 15 respectively.
(With PTI inputs)