Transport Minister Khaw Boon Wan, who has anchored Sembawang GRC for more than a decade, began thinking about passing on the baton after undergoing heart bypass surgery in 2010.

Before the election in 2015, he had set his sights on having Education Minister Ong Ye Kung succeed him as anchor minister in the group representation constituency.

Speaking to reporters at Canberra MRT station yesterday after his retirement from politics was announced, Mr Khaw, 67, said he has known Mr Ong since his civil service days at the Ministry of Trade and Industry (MTI) and described him as a "very outstanding officer".

"I was being selfish when I lobbied Prime Minister Lee Hsien Loong to get Mr Ong to come to Sembawang, so that I can hand over to him with confidence," he said. "I'm quite sure that with Mr Ong, we made the right call."

Yesterday, Mr Ong posted a tribute to his mentor on Facebook. He thanked Mr Khaw for including him in the Sembawang team and for the opportunity to lead negotiations on the US-Singapore Free Trade Agreement signed in 2003 when he was a civil servant at MTI, describing it as a turning point in his career.

Yesterday, Mr Khaw teared up as he recounted Mr Ong's tribute. "(It was) very kind of him to acknowledge the small role I played in his career. But that is the way we ought to behave as supervisors, or bosses, or managers - your job is to nurture the young."

Mr Khaw tackled hot-button issues that emerged as flashpoints in past elections, from public transport to housing. On housing and transport, he said: "Both were important, critical political problems. One was during GE2011, one was in GE2015. And if I could not deliver... I think the damage is to the party. So there was great pressure on our shoulders."

His team, he said, "dared not rest" and continued to push on.

"Fortunately, with the support of many people... (we managed to) deliver," said Mr Khaw, who added he is glad rail reliability has not emerged as an issue in this election.

As for his approach to solving complex issues, he said teamwork is key. "(If you) gather good people with the right ethos, you can make changes... this is, on a small scale, the story of Singapore."

Chuckling as he related this anecdote, he said when he told his granddaughter, who is in Primary 2, about his retirement, her immediate thought was: "Huh, there's nobody working in this family. So she says, oh, she has a solution - grandma must go and work. Then her next thought was, 'Grandpa, you must go and do marketing now. Do you know how to buy or not?'"

Reflecting on his more than 40 years in public service, he said: "It has been very satisfying - so now it's time for me to rest."