Cameron Iwasa struck a 58th-minute winner for the United Soccer League club at Bonney Field in California.
Sunderland manager Dick Advocaat started the likes of John O'Shea, Wes Brown, Lee Cattermole, Jack Rodwell, Sebastian Larsson, Jermain Defoe and Steven Fletcher.
But they were only able to break even throughout the first half, although they were perhaps unlucky not to be ahead.
