TRS tally had risen from 68 to close to 90 before the assembly was dissolved.
Confident of ousting the TRS government in Telangana, the Congress party's state chief Uttam Kumar Reddy has said Chief Minister K Chandrashekar Rao's arrogance would be the single-biggest reason for his party's rout in the assembly polls.
Asserting that the opposition alliance 'Praja Kutami' will make a clean sweep in the December 7 polls, Mr Reddy claimed the ruling TRS (Telangana Rashtra Samithi) will be contained to just 35 seats in the 119-member state assembly.
In the last assembly elections in 2014, the TRS had won 63 seats but its tally had risen further to close to 90 before the assembly was dissolved by the chief minister to advance the polls, which would have otherwise happened next year along with the Lok Sabha elections.
The TRS leaders are claiming they will get at least 100 seats this time.
Mr Reddy, who is credited to bringing the opposition alliance together, however said KCR's strategy to advance poll was a "miscalculation" and he could not see the resentment among people against his "misgovernance and autocratic rule".
"The TRS will be decimated. We will defeat KCR decisively. People are waiting to teach it a lesson for using the Telangana struggle for the personal gains. I foresee the KCR's party will be contained at under 35 seats," Mr Reddy said.
Mr Reddy, who is being seen by some as a chief ministerial candidate of the opposition alliance on account of being the state Congress president and a four-time MLA, refused to comment on post-poll scenario saying it would be decided by the Congress chief Rahul Gandhi in consultation with the elected legislators of the party.
The state Congress chief, who was an Indian Air Force pilot, said the 'Praja Kutami' alliance is unlikely to get anything less than 85 seats, while Congress alone will get 75-77 seats.
The Congress had won only 22 seats in the 2014 elections while its tally had gone further down by the time the assembly was dissolved.