Donald Trump and Hillary Clinton trade their first swings in the debate ring tonight as a new Franklin Pierce University/Boston Herald poll shows the bitter adversaries are locked in a dead-even duel, so tight even a slip-up or gaffe could sway the shrinking pool of uncommitted voters and tilt the outcome.

Clinton is ahead of Trump by just a 45-43 percent margin — a statistical tie — and a slight increase for the GOP nominee since the last nationwide Franklin Pierce/Herald poll on Sept. 4 showing Clinton up 44-41 percent.

The new poll also shows the race firming up with just 3 percent of likely voters undecided, with just six weeks left in the race. Only 15 percent of Clinton voters and 16 percent of Trump backers say they could change their minds now.

Libertarian Gary Johnson is drawing 6 percent of the vote and Green Party hopeful Jill Stein gets just 2 percent — a drop for both of them since the last poll.

The opening televised debate, the first face-to-face meeting between the two bitter rivals, is all but assured to generate huge viewership, with 86 percent of likely voters saying they definitely or probably will watch, according to the poll.

The highly anticipated showdown, the first of three, may not change a lot of minds — just 16 percent of all likely voters say the debate or even coverage of it will influence their choice for president, the poll shows.

But pollster R. Kelly Myers said even a small shift from the debate could be decisive in a race that’s likely to stay neck-and-neck all the way to Election Day.

The new Franklin Pierce/Herald poll, conducted Sept. 18-22, reveals the race has tightened over the past few weeks, despite a slew of negative stories and campaign controversies surrounding Trump. The poll surveyed 1,017 likely voters nationwide.

The billionaire real estate mogul was behind Clinton by 2.4 percentage points in the Sept. 4 poll, and now trails by just a 1.6 percent margin — which rounds out to two points. Clinton’s lead in the latest poll is well within the 3.1 percent margin of error.

All four candidates on the ballot, including Johnson and Stein, are now more disliked than liked by voters, a historic low for a White House race.

Nearly six in 10 voters view both Trump and Clinton unfavorably, and nearly half say they have a “very” unfavorable view of them, a sign of the intense sentiment dividing voters in the country.