Powell went 8 for 14 from the floor, hitting three from behind the arc, and made all eight of his foul shots.
Bruno Fernando had 19 points and 10 rebounds for the Terrapins (9-3). Coming off a 10-day layoff, Maryland fell behind early and hurt itself by going 12 for 20 from the foul line and missing 17 of 25 attempts from beyond the arc.
Cowan scored 15 and Jalen Smith had 14 for the Terps.
Maryland trailed 52-51 before Cowan hit a jumper and backcourt mate Darryl Morsell nailed a 3-pointer as the shot clock expired for a 56-52 lead with 7:50 left. The Pirates momentarily moved back in front before Eric Ayala connected from beyond the arc and Smith added a follow-dunk to make it 61-57.
But the Terrapins could not fend off the feisty Pirates. A 3-point play by Powell and two straight baskets by Cale put Seton Hall up 68-64 with 2:46 remaining.
Fernando scored 13 points, and Maryland recovered from a poor start to take a 34-30 halftime lead.
The Terrapins opened 2-for-8 shooting with three turnovers and fell behind 16-5 after Seton Hall made seven of its first 11 shots.
It was 26-21 before Fernando made a layup, a dunk and two free throws to give the Terrapins their first lead.
Seton Hall: The Pirates have the talent and the poise to make some noise in the Big East. Undaunted by losing the early lead and unaffected by playing on the road, Seton Hall stunned a Maryland team that was ranked earlier this month.
Maryland: Fernando and Smith form a formidable front court, but the opposition will surely start packing the paint until the Terrapins prove they can score from beyond the arc.
Seton Hall: Opens Big East play on Dec. 29 against visiting St. John’s.
Maryland: Concludes nonconference schedule at home against Radford on Dec. 29.
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