Long was 6 of 10 from the field and made all 10 free-throw attempts. He notched his 14th double-double this season and 66th of his career for Louisiana-Lafayette (11-8, 7-3 Sun Belt), which has won six in a row.
Tied 42-all at halftime, the game remained tight for first nine minutes after the break. But Bryce Washington's 3-point play with 10:44 remaining sparked a 10-0 run for the Ragin' Cajuns to put them in front by 14.
Erick Neal scored 14 of his 20 in the second half for Texas-Arlington (14-6, 5-4), but the Mavericks were unable to avoid their third loss in a row.
Louisiana-Lafayette opened the game on an 11-0 run and shot better than 50 percent from the floor (54.2 percent) for the sixth straight game.