Mortensen (4-3) scattered nine hits and struck out four to win his second straight start.
The Redbirds were already up by a run when Pagnozzi took Portland starter Cesar Ramos deep for a three-run homer in the second inning.
Ramos (3-4), who was taken out after 1 1/3 innings, gave up four runs, three hits and two walks while striking out one.
Jarrett Hoffpauir scored from third on a wild pitch by reliever Josh Banks in the sixth to make it 5-1 in favor of the Redbirds. Memphis added to its lead against Scott Patterson in the seventh, with Jay driving in a run on a double to left and Pagnozzi, who hit a solo homer in the ninth, drawing a bases-loaded walk.