The Firhill club conceded five goals at home against their city rivals in their penultimate league match of the 2016/17 campaign.
Archibald praised Brendan Rodgers, who made five changes to his starting line-up, for how his side had performed in the outing.
But he was bitterly unhappy with how Thistle, who have finished in the top six in the Ladbrokes Premiership for the first time this season, had performed themselves.
"We were lucky to only be beaten by five," he said. "I think they took their foot off the gas at half-time to be honest. For us, it was very disappointing.
"Celtic are obviously a good side, but you can't stand off them. We played with a fear tonight. That was there for all to see in the first five or 10 minutes. They could have been ahead before they got the penalty.
"They are more of a threat away from home. They bring an atmosphere with them. They can cut you open at any time.
"They play with a higher tempo. You can't let them play with that tempo and we did. We stood off them at key times. As I said, we gave them a gift of a penalty which sent them on their way.
"I don't think any changes they make weakens them. They play in a system and they work hard and graft whether it is 0-0 or 5-0.
"Regardless of whatever change they make it is usually like for like. Tonight it was very, very similar and they have got quality at the top end of the pitch.
"We'll be looking to play much better in our last match against Aberdeen this weekend."