Says coach Roger Cross: "It was harsh, Steve was going for the ball and made a genuine attempt to get it."
Francis Jeffers hit the post from the resultant penalty but he did equalise Richard Garcia's earlier headed goal from a Laurent Courtois corner.
After what Roger calls "poor marking" following a Scott Minto aerial clearance from another corner, Inamoto volleyed home the winner - giving the attendant Japanese journalists at Underhill something to write home about.
"I was pleased with the second half performance," says Roger, "and we came close to scoring a couple of times."
Anwar U'ddin came on for Titi Camara at half time, and Roger explains: "After Steve was sent off I needed another defender on."
Titi and Shaun Byrne had scored in the corresponding 2-1 win for the Hammers last season.
The defeat means that the reserve team have won just one game away game in seven so far this season.
Team: Andersson, Newton, Minto, Garcia, Foxe, Potts, Riza, McCann, Todorov, Camara (U'ddin 46), Courtois. Subs unused: Jackson, Ferrante, Britton, Ferdinand.