Reyna, who recently announced his retirement from international football after the USA's disappointment at the World Cup, scored the only goal in the 7th minute after being picked out on the 6-yard box by Trevor Sinclair.
Young keeper Joe Hart, signed from Shrewsbury this summer, also impressed by producing some fine saves in the 1st half.
Substitute Stephen Ireland later had a chance on the half-volley which went wide before Joey Barton and Georgios Samaras were introduced, and the Greek striker should have claimed his 4th goal of pre-season with a header.
The Blues will now head out to China for a four-team mini tournament. They face host team Shanghai Shenhua next Friday and Japanese side Kashima Antlers 2 days later. Atletico Madrid are the other participant.
City: Hart (Schmeichel h-t), Richards (Mills 76), Thatcher (Jordan 80), Distin, Dunne, Reyna (Ireland h-t), Sinclair (Samaras 72), Hamann (Laird 76), Corradi (Dickov h-t), Dabo (Barton 69), Sibierski (Miller 66).