The Black Cats fielded a side with several first-team regulars but fell behind in the eighth minute to the npower League One side when Howard finished from close range.
Sunderland were rather subdued in the first half although improved after the interval, with David Meyler shooting just wide from 25 yards. Their best chance of a leveller came when Fraizer Campbell saw his stooping header superbly tipped over the bar by Scott Flinders as Sunderland crashed to their second pre-season defeat.
Sunderland's fierce rivals Newcastle got their Trofeu do Guadiana tour under way in unusual circumstances as they and Olympiacos could not be separated - despite a penalty shootout after a 1-1 draw.
Steven Taylor, making his first appearance since December due to injury, opened the scoring in the 25th minute with a deflected strike after the Greek champions had failed to clear their lines.
Newcastle's hopes of victory increased when Francois Modeste was dismissed for a second bookable offence in the 74th minute but Olympiacos claimed an equaliser five minutes later when Kostas Mitroglou fired home from Djamel Abdoun's cut back from the left.
The clash then went to penalties, but even then the teams could not be separated after five penalties each, with Papiss Cisse missing for the Barclays Premier League outfit by blazing over the bar while Newcastle goalkeeper Tim Krul saved Andeas Tatos' effort in a 4-4 stalemate.
Source: PA
Source: PA