Referring to how such musical stars perform "flawlessly, night after night," Obama said: "I can't always say the same" -- a clear nod to his lackluster debate performance in Denver, Colorado last week.
The joke provoked sympathetic applause and laughter from the partisan packed crowd at the Nokia Theater in downtown Los Angeles, who had paid $250 dollars a ticket to attend the fundraiser-cum-show.
The Democratic incumbent was widely deemed the loser of last Wednesday's first presidential debate against Republican rival Romney, who is fighting to oust Obama from the White House in the country's November 6 election.
Obama's campaign has since then intensified attacks on Romney's honesty as it battles to halt the challenger's momentum following his unexpectedly strong debate performance.
Romney's people have hit back, sarcastically depicting Obama's team as childish sore losers after their candidate came across as flat, nervous and unassertive during the first face-to-face encounter.