Trump (48 per cent) leads Clinton (45 per cent) by three per cent in a two-way match up, CNN/ORC said.
In a four-way contest with two other presidential candidates from minor parties, Trump is leading Clinton by five percentage points.
Post conventions, presidential candidates do get a major jump in their popularity ratings.
Democratic National Convention begins in Philadelphia tomorrow, which would formally nominate Clinton as party's presidential nominee.
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Clinton's lead over Trump has been reducing every passing week.
CNN/ORC said after the Cleveland Convention, Trump has received major jump in support from independents.
Cleveland also helped Trump make strides in his personal image, the poll said.
A majority (52 per cent) now say Trump is running for president for the good of the country rather than personal gain, just 44 per cent say the same about Clinton.