The online poll shows Clinton with 47.81 percent, compared with Trump's 47.14 percent, a difference of 0.67 percent. Those responding with "others" were 5.31 percent. "Others" in the poll are defined as respondents who decline to pick either Clinton or Trump.
One day earlier, Clinton had a bigger lead of more than 2 percentage points -- 47.52 percent to 46.17 percent. And one week earlier, Clinton had 1.18 percentage point lead: 47.95 percent to 46.77 percent for Trump.
The debate will be the first head-to-head matchup of the two major parties' nominees. It will run from 9 p.m to 10:30 p.m. EDT Monday on all major broadcast and cable networks from Hofstra University in Hempstead, N.Y. The topics, as chosen by moderator Lester Holt, are "America's Direction," "Achieving Prosperity," and "Securing America," per a release from the Commission on Presidential Debates.
The UPI/CVoter online tracking poll surveys more than 200 people each day, leading to a sample size of at least 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. 19 to 25, when 1,572 individuals were surveyed. Of them, 1,052 identified themselves as likely voters.