In 2011, all but one of the GRCs were contested. This time, with all the 16 GRCs seeing electoral fights, which are the ones to keep an eye on? The Straits Times narrows it down to those that will see clashes between the PAP and leading opposition party, the WP, as well as the GRC that will be contested for the first time.
EAST COAST GRC
Could this be the Aljunied GRC in this general election (GE), changing its hue from white to blue?
What is certain is that the fight in East Coast GRC will be the most closely watched, as the Workers' Party (WP) is likely to send its second "A" team - next in line to the "A" team that party chief Low Thia Khiang successfully led to victory in Aljunied GRC in 2011 - to the constituency.
In the last election, East Coast GRC saw the narrowest win for a GRC for the People's Action Party (PAP), with 54.8 per cent of the vote.
WP's Gerald Giam is expected to return and lead the team again, this time with an elevated profile after four years as a Non-Constituency MP. The three others are likely to be selected from among these four: sociologist Daniel Goh, law firm partner Dennis Tan, research and consultancy firm chief executive Leon Perera, and librarian Mohamed Fairoz Shariff.
They will be up against the PAP slate headed by Manpower Minister Lim Swee Say, who has said he wants to return to the GRC. In his corner: office-holders Mohamad Maliki Osman and Lee Yi Shyan, plus Microsoft Singapore managing director Jessica Tan.
There was a buzz last night as about 80 activists and volunteers gathered at Mr Lim's Bedok ward for a pow-wow on election logistics.
The stakes are high for the PAP. Said its youth wing branch chairman Leong Yi Xing: "We see ourselves as one of the lines of defence.
"Imagine if East Coast and Aljunied both go that way (to the WP), then it opens up the way for them in the eastern region.
"Just adjacent to us, we have Pasir Ris-Punggol GRC, a lot of the SMCs. If we can hold the ground here, at least we can act as a buffer between Aljunied and the rest."
The PAP incumbents have been cautious about publicly commenting on the challenge, with the usually affable Mr Lim telling The Straits Times he will respond only after his team is formally introduced tomorrow.
Similarly, WP chairman Sylvia Lim said yesterday it would not be making any comments as yet. The party will begin introducing its candidates today.
Another hint that the ruling party had taken stock of the challenge: Fengshan ward - viewed as the GRC's weakest link - has been hived off as a single-seat constituency. The GRC is now the smallest, with 99,015 electors.
How the battle may go will depend on which narrative appeals to the hearts and minds of the voters.
The PAP team has emphasised its hard work on the ground, with residents praising the slew of new and upgraded projects.
Even Mr Giam has chimed in with bouquets for his rival, Ms Tan, saying in a Facebook post that "Jessica's work at the local and town level is certainly something we look to emulate".
But, in an indication that the WP team will fight the battle at the national level, he added, a general election is "about more than just voting for a local MP".
"It's also about ensuring that the people have bargaining power to make the government more responsive to people's needs," he wrote, arguing that new measures to improve citizens' welfare were a result of the last GE.
The argument however may not be as effective as in 2011, when the WP put all its top guns in Aljunied GRC, placing the onus on the residents to ensure opposition representation in Parliament.
This time, all its seven MPs are defending their constituencies.
But with half of East Coast GRC's voters from public housing and the other half in private homes - a group that traditionally is more sympathetic to the opposition's argument for greater checks and balances, it is likely to be GE 2015's hottest ward.
MARINE PARADE GRC
In 2011, public attention here focused on two young women in opposing teams: National Solidarity Party's telegenic Nicole Seah and PAP's Tin Pei Ling who was caught backfooted in a party video.
In the end, the PAP garnered 56.6 per cent of votes, the second-lowest for a GRC. It was a shock result as the incumbent team was headed by Emeritus Senior Minister Goh Chok Tong while the NSP team was relatively unknown.
This time, both women are gone from the GRC. Ms Seah has quit politics while Ms Tin is contesting on her own in MacPherson.
But other changes have ensured the temperature in the GRC remains relatively high. One, Joo Chiat - which in 2011 saw the PAP win by a whisker of 388 votes, has been absorbed into the GRC.
But more significant is that the WP - the most credible opposition party - is taking the place of the NSP in challenging the incumbents.
The WP team is expected to comprise Non-Constituency MP Yee Jenn Jong, lawyer Terence Tan, chocolate factory owner Firuz Khan, corporate lawyer He Ting Ru, and wealth manager Dylan Ng.
Speaking at a residents' barbecue event last night, Mr Yee said he had asked the WP leadership to stay and contest in the area. "I asked for a committed team, which I got," he said.
Like in East Coast GRC, there will be no new faces in the PAP team. It is led by Social and Family Development Minister Tan Chuan-Jin, and includes ESM Goh, NTUC FairPrice head Seah Kian Peng, lawyer Edwin Tong and doctor Fatimah Lateef.
On whether the team expects a tougher contest with WP, Mr Seah would said: "We take every party that comes seriously."