The People's Action Party (PAP) triumphed over Barisan Sosialis in the Hong Lim by-election this week in 1965. At stake was the Legislative Assembly seat which fell vacant when one-time PAP minister Ong Eng Guan resigned abruptly in mid-June.
Mr Ong and his United People's Party came out in support of Barisan during the campaign.
The PAP candidate was Mr Lee Khoon Choy, political secretary to the Prime Minister, while Barisan fielded Mr Ong Chang Sam, its organising secretary.
Both parties ran charged campaigns in the lead-up to polling day, holding street rallies, televised talks and radio addresses.
The by-election could have been a huge blow to the PAP, had it lost.
Many in the PAP believed that Mr Ong's resignation had been engineered by Malaysia's main Malay party, Umno, and that the forced by-election would be a litmus test of support for the PAP and its "Malaysian Malaysia" cause.
These suspicions were heightened when Umno threw its support behind Barisan openly, even though it was a pro-communist party that often used the slogan "Crush Malaysia".
In a televised talk, Barisan chairman Lee Siew Choh said the PAP's "Malaysian Malaysia" was "a selfish PAP slogan, a communal slogan and a neo-colonialist slogan".
During a rally in Nankin Street, PAP leader Lee Kuan Yew said Barisan wanted to destroy Malaysia but would need Indonesia's help to do it since the party had no weapons. He added that once Malaysia was destroyed, Indonesians would pour in and "loot the nation".
Hong Lim voters cast their ballots on July 10 at one of seven polling stations from 8am to 8pm, after which the ballot boxes were taken to Victoria Memorial Hall for the votes to be counted.
The PAP's candidate won decisively by more than 2,000 votes, receiving 6,398 votes to his opponent's 4,346.
With that, the PAP's presence in the Legislative Assembly increased to 38 seats, with Barisan holding the other 13.
The defeated Mr Ong thanked his supporters for their "courage despite the threat and intimidation by the PAP Government". He added that the by-election was a snap affair, and the PAP Government had given the opposition only nine days to prepare for it.
The winner, Mr Lee Khoon Choy, said his triumph "shows that the people of Singapore reject a communal Malaysia". He added: "We hope that the results of the Hong Lim by-election will be a lesson to those who think they can bulldoze communal politics down the throat of Malaysians."