The Trail Blazers have won two in a row on the road after falling in 14 of their previous 17 contests away from home.
Portland trailed by three heading into the fourth period, then pulled away thanks in part to a strong showing from Matthews. He hit 5-of-8 from 3-point range and finished with 28 points.
Damian Lillard added 22 for the Trail Blazers and LaMarcus Aldridge had 20.
Atlanta, which has dropped two of three, was led by 24 points from Josh Smith.
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