It was Ellis' third double-double of the season.
Farad Cobb had 16 points, Jermaine Sanders added 12 and Gary Clark 11 for Cincinnati (22-9, 13-5). The Bearcats made 50 percent of their 48 field goal attempts and went to the line 29 times compared to Memphis' 15.
Cincinnati jumped out to a 21-4 advantage midway through the first half and held on for a 34-21 lead at halftime behind Cobb's 10 points.
Cincinnati and fifth-seeded Memphis will both have first round byes and will play in quarterfinal games on Friday.