YSRCP was leading in 145 seats in the state's 175-member Assembly while the Telugu Desam Party (TDP) was ahead in 28 constituencies.
Actor Pawan Kalyan's party Jana Sena was leading in two constituencies, according to information available with the Election Commission.
Jagan Mohan Reddy's party was racing ahead across the state from the time the initial trends started emerging.
YSRCP also appeared to be making a clean sweep in the Lok Sabha polls as the party was leading in 24 of the 25 constituencies.
The results came as a huge shock to TDP chief Chandrababu Naidu, who was not only confident of retaining power in the state but was hoping to play the role of kingmaker at the Centre.
In 2014, the TDP had bagged 102 seats while its then ally BJP had won four seats. The YSRCP had won 67 seats while two independents were also elected.
In the Lok Sabha elections held simultaneously, the TDP had won 15 and the BJP two seats. The YSRCP bagged the remaining eight seats.
The trends so far show that BJP and Congress are not leading in any of the Assembly or Lok Sabha seat. No change in fortune is expected for Congress, which drew a blank in the simultaneous polls in 2014.
( With inputs from IANS )