Donald Trump is gaining support among African-American voters — whose enthusiasm for Hillary Clinton is eroding, a tracking poll released Saturday revealed.

Trump saw a 16.5 percentage-point increase in backing from African-American voters in a Los Angeles Times/University of Southern California tracking poll, up from 3.1 percent on Sept. 10 to 19.6 percent through Friday.

Meanwhile, the same poll showed Clinton’s support among that group plummeting from 90.4 percent on Sept. 10 to 71.4 percent.

Clinton’s nearly 20-point crash began Sunday, said Dan Schnur of USC. Sunday was the day Clinton was recorded collapsing while entering a Secret Service van at a 9/11 event.

The survey, which spanned through Friday, included the days in which Trump reignited the divisive “birther” issue — which critics contend is a thinly veiled attempt to undermine the legitimacy of the country’s first black president.

Late Wednesday, Trump had refused to acknowledge that President Obama was born in the United States, demurring on the topic in a Washington Post interview published the next day.

But at a bizarre press conference at Trump International, his new ­hotel in Washington, DC, on Friday, the tycoon conceded, “President Barack Obama was born in the United States, period.”

For the week, the poll found a 6-point rise for Trump. The Republican is now at 47.2 percent of the vote to Clinton’s 41.2 percent.

“It’s the largest shift we’ve seen in a one-week period since we began polling in July,” Schnur said.