Williams was unable to name a full substitutes' bench after Stephen Purches fell ill on the day of the game and there were no other fit players available to take his place.
Orient's resistance lasted until first-half injury time and three more Huddersfield goals in the second period made it an afternoon to forget for Williams.
The O's manager said: "What cost us was we switched off for 30 seconds just before half time and we conceded a goal. A goal at that stage of any game changes what happens in the dressing room at the break.
"I ended up feeling that we didn't have the right mentality to go out in the second half and score twice.
"We went on to lose our shape and discipline in the second half. I was disappointed by both that and how Huddersfield scored three of their goals."