NSU (9-12) had five combined errors in three different innings and in those three frames, the Sooners (17-4) scored seven of their runs.
OU held a 5-0 lead after the sixth inning, but the Demons cut it to 5-3 in the seventh before Oklahoma added three more in their half of the frame.
Sooner starter Adam Choplick (3-0) took the win over NSU's starter Joey Parrack (0-3) who was tagged with the loss. Jacob Evans (4) got the save after coming and halting the Demons' rally inning.
Choplick worked 6.2 innings and allowed one run on three hits with eight strikeouts. Parrack pitched 2.2 innings and gave up three hits and three runs (one earned) with three walks and three strikeouts.
Three Demons had hits on the day; Edwin Gomez had two, and Nick Purdy and Todd Wallace each had one.
OU had 11 hits, and were led at the plate by Matt Oberste who was a perfect four-for-four on the day with a run batted in and two runs scored. Kolbey Carpenter had two runs batted in on a one-of-four day.
Edwin Gomez led off the seventh inning with a single through the right side. After Jake Clouatre lined out to shortstop, Gomez took second on a wild pitch.
He took third when Matt Baca grounded out to second base and scored on a second wild pitch.
Zack Costa and Mitch Huckabay scored after Cort Brinson hit a fly ball to second baseman Hector Lorenzana who dropped it.
The Demons will return home to open Southland Conference play with Southeastern Louisiana.