The National Solidarity Party (NSP) pulled off a surprise yesterday by fielding a candidate in MacPherson, thus setting up a three-cornered fight for the single seat, now held by the People's Action Party (PAP).

This latest twist to the on-and-off, then on again, three-way contest not only breaks up the straight fight between the PAP and Workers' Party (WP), but also threatens to dilute the opposition vote-share at the Sept 11 polls. This may just tilt the scale further in favour of PAP candidate Tin Pei Ling and work against WP newcomer Bernard Chen.

But the WP will no doubt view the appearance of NSP veteran Cheo Chai Chen yesterday as a rejoinder to the dominant opposition party's perceived high-handedness during multi-party talks to avoid such three-way contests.

The NSP during the talks had given up Marine Parade GRC to the WP on the presumption that, in return, it would get to enter into a straight fight with the PAP in MacPherson SMC. The NSP had contested Marine Parade GRC in 2011 but lost to the PAP, which garnered 56.64 per cent of the votes to the NSP's 43.36 per cent.

The battle for the SMC, which was part of Marine Parade GRC, is this General Election's only contest involving three political parties.

Two other similar contests - in Bukit Batok and Radin Mas - each involves the PAP, an opposition party and an independent candidate.

The three-way fight for MacPherson, which was touted earlier last month after the NSP unexpectedly threw its hat in the ring, had seemed increasingly unlikely after NSP's repeated flip-flops before Parliament was dissolved last Tuesday.

NSP chief Hazel Poa had quit the party in protest over its decision to field a candidate in MacPherson.

While it was widely expected that the WP would field Mr Chen, who is 29, against the 31-year-old Ms Tin, Mr Cheo was never thought to be in the fray. The 64-year-old arrived at the nomination centre in Kong Hwa School yesterday and almost slipped past the media unnoticed.

He told reporters before making his way into the school: "I've participated in elections many times before and this one is nothing special.

"This election will require more experienced candidates. It would be harder for new people."

When asked whether his nomination was a last-minute decision by the NSP, he said: "It's a long story."

Mr Cheo - a former opposition MP from 1991 to 1997 - and Mr Chen will attempt to prise the single seat from Ms Tin at the polls.

As the youngest PAP candidate to be fielded at GE2011, Ms Tin came under heavy fire because of her youth and inexperience. But Ms Tin, who gave birth to a boy just three weeks ago, managed to cement her position in the ward since her debut four years ago at just 27.

Once again the PAP's youngest candidate, Ms Tin said yesterday she is ready for the fight - whether it is against one or two challengers. "We have been here over the years, we'll continue to be here and we are the best party that will fulfil and that can fulfil our promises."

Mr Chen, an executive with a funeral services provider, said he hopes voters will give him a chance to serve them. "Your small matters are big matters to me," he said in Mandarin during his speech.

Political observers like law don Eugene Tan said Mr Cheo is unlikely to have significant impact on the contest for MacPherson SMC. "Although it's a three-cornered fight, it will be in substance a straight fight between PAP and WP."

There was also palpable discontent among WP supporters over the NSP's decision to field Mr Cheo.

Taxi driver Tan Poh Peng, 42, said: "I'm not worried about the three-cornered fight here because I believe NSP has no chance here."

•Additional reporting by Lim Yi Han and Lydia Lam