Perry gave a free concert at a park in a historically minority neighborhood just northwest of downtown Las Vegas to screaming fans at about 9 p.m., the same time Air Force One landed at McCarran International Airport across town.
Obama later told the crowd, "I believe in you. I need you to keep believing in me."
The Las Vegas campaign event drew more than 10,000 people, according to fire officials and organizers, with long lines still on sidewalks during Perry's 30-minute performance before Obama arrived.
The singer opened with a rendition of Al Green's soul hit, "Let's Stay Together," and played five songs, including "Teenage Dream," before ending with a thumping bass drum version of "Firework."
Perry, who recently also played a free concert at an Obama event in Los Angeles, paused before the last song Wednesday to exhort people in the Las Vegas crowd to vote early.
"Don't wait. Go tomorrow," she said. "How many of you are 18 here? It's going to be your first time, right?"
Copyright 2012 The Associated Press. The information contained in the AP news report may not be published, broadcast, rewritten or otherwise distributed without the prior written authority of The Associated Press. Active hyperlinks have been inserted by AOL.
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