Chelsea had come from behind to lead in Philadelphia, only to concede an equaliser and then an injury-time winner against the pick of the US league, which included both David Beckham and Thierry Henry.
"We're disappointed with the result, we are always looking to win and we were a little bit stretched in the second half," Di Matteo told chelseafc.com. "I made some changes and the team was maybe not as together as in the first half where it was a bit more settled.
"The MLS team looked very sharp and were obviously in season so looked sharper than us. For us it was important to get players on the pitch and as many minutes as possible. We have to look to improve the way we play a little bit but I was happy with the play in the first half and it was a good test for us."