Hillary Clinton has opened a nine-percentage-point lead over Donald J. Trump in Florida, according to a new poll released on Tuesday that shows minority voters and women buttressing her presidential campaign.

The survey from Monmouth University found that 48 percent of likely voters support Mrs. Clinton, while 39 percent back Mr. Trump. Gary Johnson of the Libertarian Party trails with 6 percent and the Green Party’s Jill Stein has 1 percent.

The margin is wider than other Florida polls that show Mr. Trump trailing by about four points in the state, where he maintains a residence and scored a resounding victory in the primary election. With Mrs. Clinton leading in several battleground states, Florida could prove essential for Mr. Trump’s chances in November.

“The gender split among white voters in Florida is huge,” said Patrick Murray, director of the Monmouth University Polling Institute. “Men are drawn to Trump’s message while women are not. These offsetting factors give Clinton the edge.”