A YouGov survey of more than 1,000 Londoners found 53 per cent of likely voters favoured Khan, compared to 47 per cent backing Goldsmith.
The poll found that Khan has a particularly strong lead (57 per cent) among female likely voters. Male respondents were more evenly split.
Meanwhile, older voters proved more partial to Goldsmith, with 58 per cent backing the Richmond Park MP. Among younger voters, however, Khan came out overwhelmingly on top, with 71 per cent of likely voters between the ages of 18 and 24 saying they backed the Tooting MP.
The results of the poll first appeared in the Evening Standard.
The two candidates are set to square off tonight at a dinner hosted by the Federation of Small Businesses in Marylebone, where each is expected to make his case to an audience of the capital's leading business figures.