Memphis is the first unanimous Number-1 in the Associated Press' men's basketball poll since Florida did it for two weeks last February on the way to a second straight national championship.
The only unbeaten team in Division I received all 72 first-place votes from the national media panel.
Duke and North Carolina, who meet Wednesday night in Chapel Hill, moved up one spot to second and third. Kansas, which suffered its first loss last week, drops from second to fourth.
UCLA is fifth, followed by Georgetown, Tennessee, Wisconsin, Stanford and Butler.
Michigan State slips from eighth to 11th and is followed by Texas, Xavier, Indiana, Drake, Marquette, Washington State, Texas A&M, Connecticut and Kansas State.
Pittsburgh, Notre Dame, Vanderbilt, Purdue and Saint Mary's are the last five ranked teams.
Connecticut, Notre Dame and Purdue are all making their first Top-25 appearances of the season, replacing Florida, Mississippi and Baylor.