Congress wrestled the Valpoi seat in the by-poll on Thursday with its candidate Vishwajit Rane winning the election by margin of over 8,000 votes.
Bharatiya Janata Party's Santosh Haldankar was defeated in the poll, which saw Congress winning over the seat comfortably.
Congress polled 11,642 votes and BJP could get only 3,237 votes.
The counting for the by-poll began at 0800 hours on Thursday morning at Campal near here. The polling had taken place at October 18 for this crucial seat.
For the first round, Rane led with 3,000 votes polling almost 90 per cent in the Valpoi city, which is considered as Congress stronghold.
Rane increased his lead to 5,878 votes after second round of counting and his victory was confirmed.
Total 14,881 voters had cast their votes notwithstanding the rains that hit this rural taluka.
Congress had contested the poll on development issue while BJP had asked for votes claiming that Rane was encouraging mining in this taluka ruining the greenery.
The by-poll in this constituency was necessitated after Rane, state's health minister and independent candidate, resigned as Member of Legislative Assembly and joined the Congress on June 24, 2010.
After losing the elections, Haldankar said that increasing use of money by Rane engineered his defeat.
"There was massive use of money power. We could not counter this power," he said.
On the other hand, Rane said that the development, which he has done in this constituency paid off.
"People voted for the development. The constituency had suffered last time when they voted for BJP," he said, adding that people have realised that only Congress can give proper governance.
Goa Chief Minister Digamber Kamat, talking to reporters at counting centre, said that Valpoi voters took right step by supporting Congress.
"Vishwajit was not new to people and Congress. His entry has consolidated Congress' strength in the state," he said.
With Thursday's result, Congress has increased its strength in Goa legislative assembly to 20 in the 40-seat House.
The BJP has 14 members, two of Maharashtrawadi Gomantak Party, three of Nationalist Congress party and an Independent legislator.
