Nearly 20,000 fans filled Quicken Loans Arena for the "Last Chance for Change" rally, which began after Obama's 30-minute TV ad was shown on a giant screen above the stage.

Wearing a black leather jacket, baseball cap and huge diamond chain in the shape of Ohio, James encouraged the crowd to participate in next week's election.

"I want everybody in here, moms, dads, aunts, uncles to get out and vote," James said. "November fourth is the most important day of our lives."

He then introduced Jay-Z, a close friend for years who tore through some of his biggest hits including "Roc Boys," "Give It To Me," "Dirt Off Your Shoulders," "Show Me What You Got" and "99 Problems."

As Jay-Z spit out lyrics, James danced and bounced around the stage in front of some of the same Cleveland Cavaliers fans who cheer his every move on the hardwood.

Jay-Z, whose real name is Shawn Carter, also used the occasion to support Obama's candidacy.

"Rosa Parks sat so Martin Luther King could walk, and Martin walked so Obama could run," the rapper said. "Obama is running so we all can fly, so let's fly."

Earlier this month, James attended a downtown rally to encourage people to vote early. He's also contributed $20,000 to a committee supporting Obama.

The crowd was filled with many first-time voters, who were reminded that they can submit their ballots early.

"I voted two weeks ago with some co-workers," said Patricia Hockett, a 50-year-old Cleveland woman who was thrilled to see so many young people excited by the election.

She said James' activism and Jay-Z's appearance will help energize the youth vote.

"It's wonderful," she said. "These kids respect LeBron. They look up to him, respect and believe what he has to say."