The two candidates for Bukit Batok have begun pounding the streets in the single-member constituency to woo its 27,000 voters.
Both Singapore Democratic Party chief Chee Soon Juan, 53, and People's Action Party branch chairman Murali Pillai, 48, continued their house visits last night.
Though the date for the by-election has not been announced, both teams say they are trying to cover as much ground as they can in the days and weeks ahead.
The single seat's 45,000 residents were left without an MP when Mr David Ong resigned over an alleged affair with a grassroots volunteer.
SDP introduced Dr Chee as its candidate on Sunday and the PAP announced Mr Murali, a lawyer, as its pick on Monday.
Yesterday evening, Dr Chee congratulated Mr Murali on being selected when he met reporters ahead of house visits. "He is a very able person to represent the PAP in this by-election," he said. "I look forward to having a good contest with him."
Dr Chee said he would speak up on issues like jobs and the poor.
He also said his edge over Mr Murali, a grassroots volunteer in Bukit Batok for over 16 years, is that his would be an alternative voice in a PAP-dominated Parliament.
"I just don't see how Mr Murali is going to be different from his other 81 colleagues," he said.
He cited last year's hepatitis C outbreak at Singapore General Hospital, and noted that officials have not named the people involved, despite there being several deaths.
"There's been a dearth of accountability and I think that's where we come in and can make a difference that Mr Murali cannot," he said.
Dr Chee led the SDP team to contest Holland-Bukit Timah GRC at the 2015 General Election and it won 33.4 per cent of the votes.
The SDP candidate for Bukit Batok, Mr Sadasivam Veriyah, won 26.4 per cent of the votes, while the PAP's Mr Ong received 73 per cent.
Mr Murali was in the PAP team contesting Aljunied GRC in GE2015 that won 49 per cent of the votes.
He told The Straits Times before house visits yesterday that he had a busy schedule to reacquaint himself with residents. Mr Murali, who was PAP's Bukit Batok branch secretary before he moved to Paya Lebar ward in 2012, said his focus was to "meet with residents and have some face-time with them".
"The reception has thankfully been warm, and the more senior people remember me," he said. "It's always nice to catch up with them."
Mr Murali would not be drawn into commenting on his rival, but Emeritus Senior Minister Goh Chok Tong said in a Facebook post: "Murali is humble and not egoistic; sincere and not opportunistic; a committed doer and not a smooth talker; an honest man and not a born-again politician. I will back him anytime."
Dr Chee said he found it insulting that Mr Goh would use characterisations, and would prefer to focus on the issues.
Retired engineer Lee Yifang, 72, said he backs the PAP, as it has always met his needs, but said PAP MPs had to "learn their lesson and not fool around".
Another resident, who wanted to be known only as Wu, said: "The PAP has been good with its policies, but it is important to have an alternative voice in Parliament so that real residents' voices are reflected."
Residents like salesman Wilson Sng, 46, are undecided: "When these candidates come along, I'll ask what each of their plans are to reduce the noise coming from the MRT station. Maybe that is what will decide my vote."