Odion Ighalo slammed home the opener via the underside of the bar from 20 yards just before the half-hour, and Daniel James added a second with a sharp run and finish just before the hour mark.
Juan Mata bagged a third eight minutes from the end and Mason Greenwood and Andreas Pereira struck in injury time, as United extended their unbeaten run to 11 matches, with nine clean sheets in that time.
The game was played without fans in line with the guidance of the Austrian government -- one of four matches to be held behind closed doors on Thursday.
UEFA on Wednesday confirmed that the first legs between Inter Milan and Getafe in Italy, and between Sevilla and Roma in Spain, would not go ahead as planned.