The online poll shows Clinton with 47.86 percent, to Trump's 47.69 percent, a virtual tie.
The most recent data reflect a 0.41 percentage point shift up for Clinton, while Trump stayed the same compared to data collected a day earlier.
Wednesday's results reflect the first polling conducted after Monday's first presidential debate. Flash polls conducted by CNN and others immediately after the debate rated Clinton the winner of the event, which focused on the economy, race relations and the candidates' records.
It drew the largest debate audience in history.
The UPI/CVoter online tracking poll surveys about 200 people each day, leading to a sample size of roughly 1,400 people during any seven-day span.
Because the poll is conducted online and individuals self-select to participate, a margin of error cannot be calculated. The poll has a credibility interval of 3 percentage points. This seven-day span includes data collected from Sept. 21 to 27, when 1,822 individuals were surveyed. Of them, 1,239 identified themselves as likely voters.