Congress had won 32 seats in the 2008 Assembly elections in the Christian-dominated state.
Counting in one seat, Lawngtlai East, could not be completed because of a problem in an EVM at Tialdawngilung polling station, Joint Chief Electoral Officer H Lalengmawia told PTI.
A repoll would be held on December 11 and counting on December 12, he said.
In Serchhip, Thanhawla, who was elected to the Assembly for a record ninth time since 1978, won by a margin of 734 votes defeating his nearest Mizo National Front (MNF) rival Lalramzauva, who got 4,985 votes in a four-cornered contest.
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In Hrangturzo, the Chief Minister defeated his Mizoram People's Conference (MPC) rival Lalthansanga by 1,638 votes. Thanhawla received 5173 votes in a five-cornered contest.
Thanhawla had been chief minister in 1984, 1989, 1993 followed by a break for two terms before he donned the mantle again in 2008.
Finance Minister H Liansailova was defeated in Aizawl North-II by Lalthanliana of MPC, a junior partner of MNF.
Tourism Minister S Hiato lost to MNF's K Beichhua in Saiha.