Along with Ionescu's 21, the Ducks had double-digit points from Ruthy Herberd's 16 with 15 from Maite Cazorla, Oti Gildon added 11 and Lexi Bando had 10.
The Ducks shot 45.9 percent on 28-of-61 including canning six 3-pointers and were 15-of-16 from the free throw line.
Maryland, which was the No. 3 seed in the East Regional 45.6 percent on 26-of-57 but missed all six of its 3-point shots and were 11-of-17 from the charity stripe.
The Ducks win by the Ducks marks the highest placing that Oregon has ever had in the NCAA Women's tournament.