Moyes said: "It was a difficult afternoon, and in the second half of the season we've probably had too many difficult afternoons.
"We just looked as if we were lacking real mental toughness and leadership out there today, which is obviously disappointing.
"The manager will always be the one who gets questioned and asked about what you do in these situations, but this is the same team that played against Liverpool last week and drew 2-2.
'We had to come and do a similar job to last week, but defensively and the jobs in front in midfield were so badly done today, which made it really difficult.
"People want us to play with our best players, which we're trying to do, but it's exposing other areas of the pitch.
"Maybe we haven't quite got the right organisation, and the players don't work quite right in such a strict structure.
"Over the last three years I think there's been a really strict structure here, but it's got us good results and it's got us European football. Today, our structure was so poor, players were out of position, and they didn't do their jobs well enough.
"We've probably played 12, 13, 14 more games than some other teams this season, which does have an impact, but we had a whole week to prepare for this game.
"I've said all along how difficult it is to play Thursday-Sunday, so I can't back that up today with the way we've performed. Chelsea played Tottenham in midweek, and then were right at it again today.
"Chelsea are in a good moment, let's be fair. They started the season poorly and have picked up, while we started the season well and have now found ourselves not in a good run in the second half of the season."