The event took place at Manhattan's Apollo Theater late Thursday, when Obama stepped up to the podium and veered from prepped remarks to thank Al Green for a performance that warmed up the crowd.
That's when the president launched into "Let's Stay Together," singing, "I, so in love with you" - complete with vibrato.
He stopped to laughter and applause, and remarked that his staff didn't believe he'd do it.
Then he noted that the Sandman hadn't come out - a reference to Sandman Sims, the tap dancer who chased unpopular acts off-stage at the Apollo for decades.
In addition to the New York fundraisers, the president also had a private meeting at the home of director Spike Lee.
The Associated Press contributed to this report.
