Both men voted early this morning: Khan in his multiethnic constituency of Tooting in south London, and Goldsmith in his leafy, affluent southwestern suburb of Richmond.
While there are 12 candidates in the London race including those running for the Greens, Liberal Democrats and Women's Equality Party, Khan and Goldsmith are between 12 and 14 points ahead.
Their different backgrounds have provided a key framework for the race. Khan, 45, is lampooned for how often he repeats his "son of a bus driver" refrain and grew up in social housing with Pakistani immigrant parents, where he slept at home while studying law in order to save for a house. He worked as a human rights lawyer before entering politics.
Goldsmith, 41, is the son of billionaire financier James Goldsmith and edited The Ecologist magazine before entering politics where he serves as MP for Richmond. His strong green credentials have seen him endorsed by London's popular Evening Standard newspaper who said he has the more "compelling ideas on tackling pollution and congestion".
For voters, the key issues are housing and transport in a city where many struggle to find an affordable place to live and commuting for an hour or more is common.
"Muslim or non-Muslim, it doesn't ... matter for the community," said 57-year-old Koyruz Zoman, a Muslim cook from Whitechapel in the ethnically diverse East End.
"Whoever comes in, we want what they've promised."
Human Resources manager Leeanne Collaco, 28, said religion was not as important as someone who has "known struggles".
"He probably would fight harder for a fairer London," she said of Khan.
The London vote takes place on the same day as regional elections in Scotland, Wales and Northern Ireland which are expected to leave the balance of power in the regions broadly unchanged.
However they will be a key test for Labour leader Jeremy Corbyn - a veteran socialist elected to lead the party against David Cameron is September in a groundswell of young support, similar to that experienced by Bernie Sanders in the US at present.
Both Labour and the Conservatives are dealing with internal divisions in their parties. Labour between the moderate and hard-left under Corbyn and the Conservatives between those who want Britain to stay in the EU and Eurosceptics who want out ahead of the June 23 referendum.
In the Scottish Parliament, First Minister Nicola Sturgeon's pro-independence party is looking to tighten its hold on power as it seeks to build support for a second vote on leaving the UK following a failed referendum on the issue in 2014.
If Britain as a whole votes to leave the European Union but Scotland votes to stay in, Sturgeon says that would be a pretext for her Scottish National Party to demand another independence referendum.
In Wales, polls put Labour on course to retain their dominance in the Welsh Assembly, with the Conservatives and nationalists Plaid Cymru vying for second place.
In Northern Ireland, the delicate balance in the power-sharing executive set up after decades of sectarian violence also looks set to continue.
