Spurs went down 1-0 in Belgium with Lior Refaelov capitalising on a Ben Davies error to score the only goal of the game.
Gareth Bale was named in the side after not featuring in the 1-0 victory over Burnley at Turf Moor, while Dele Alli, Harry Winks and Giovani Lo Celso also came into the side.
And Mourinho could not hide his anger at those players failing to grasp their opportunities to hand him a selection dilemma.
"We got what we deserved. We let them win, I can say that,â Mourinho said.
"I would like to make 11 [changes at half-time]! I didn't make five as was afraid of a long 45 minutes.
"At half-time I tried to improve the situation but was not enough. Second half we improved. In the end Antwerp got what they deserved.
"The best team won and the worst team loss. After tonight, my future choices are going to be very easy.
"Before matches you always ask me why this player is not playing, why this player is not playing, why this player is not selected.
"Maybe now for a few weeks you don't ask me that because now you know the answer."