FOUR years ago, they were doctor and patient. Mr Sean Lien was shot in the face when a gunman opened fire at a campaign rally in 2010. Dr Ko Wen-je, 55, who is an emergency room doctor, is credited with helping to save the life of Mr Lien, 11 years his junior.

On Saturday, the two men - Mr Lien of the Kuomintang (KMT) and Dr Ko, running as an independent - are facing off in a key race to become the next mayor of Taipei.

The capital is a crucial battleground in Taiwan's local elections, where 18 million voters will choose from 20,000 candidates to fill a record 11,130 posts ranging from municipal mayors to township chiefs. In particular, the six mayoral races will be closely watched as a litmus test for the 2016 presidential election.

There will be implications for cross-strait relations, given that a KMT defeat will hobble President Ma Ying-jeou for the rest of his term.

Eyes will be on Taipei. The high-profile post is viewed as a stepping stone to the presidency - all Taiwan's elected presidents, from Mr Lee Teng-hui and Mr Chen Shui-bian to Mr Ma, have served as the capital's mayor.

Though a KMT stronghold, Taipei looks likely to fall to the pan-green camp - represented by Dr Ko - for only the second time in history. The last time was in 1994 when Mr Chen of the pro-independence Democratic Progressive Party (DPP) became mayor.

Polls consistently show Dr Ko, son of a teacher, to be ahead of Mr Lien, who had started off with far greater name recognition. His father is Mr Lien Chan, who had served as both vice-president and premier of Taiwan and is now honorary chairman of KMT.

In a phone interview with The Straits Times from Taipei on Friday, the bespectacled Dr Ko puts his advantage down to his "lack of political burden". He is not formally affiliated to any parties though he is supported by the DPP.

He has also shrewdly parlayed his status into an election platform that includes promises to "break down the tall wall between the blue and green camps", in formulating and executing policies.

It is catnip to an electorate long weary of dysfunctional partisan politics and party infighting.

Dr Ko says he will not join any party if elected. He will also demand that "first-tier government employees" in his administration refrain from taking part in political party activities.

"We will have an open attitude and talk to any of the political parties," he says. "We will also work at getting the widest public support (for policies) as back-up - no one will want to go against what the people want."

Mr Lien, who studied law but worked in the financial industry, is positioning himself quite differently. In an e-mail response to questions, he remains upbeat about his prospects, saying polls are just "snapshots" and that the real test is in today's vote.

With his "years of financial experience", he is better positioned than his rival to tackle Taiwan's biggest challenge - to regain its economic competitiveness.

"Taipei is Taiwan's financial heart, and voters care about housing, jobs, wages (and so on). My financial background is my strength; the people want a more prosperous Taipei and I think that's why voters support me."

Asked about this, Dr Ko shoots back: "I also don't think that Mr Lien has an understanding of the economy. In reality, he has no experience in that area, neither was he trained in economics; he was in fact, just a law student."

The campaign has, thus far, been marked more by mud-slinging and sniping on both sides than any substantive discussions of issues. In particular, the senior Mr Lien has been criticised for insinuating that Dr Ko's grandfather, a school principal, was a traitor for working for the then Japanese colonial regime.

This is despite the shared experience of the two men in 2010.

Mr Lien was stumping for a KMT candidate when a gang member shot at him. The attacker said he had been targeting the candidate over a personal dispute but hit Mr Lien by mistake.

Dr Ko, then head of the trauma department at National Taiwan University Hospital, coordinated Mr Lien's treatment.

Though he thanked Dr Ko for "helping me through my life crisis", Mr Lien, speaking at a pre-election press conference, added: "He was probably not the most vital person during the procedure."

WITH ADDITIONAL REPORTING BY PEARL LIU