A mistake by Clark seconds before the interval resulted in Carlos Tevez sealing City's seventh away win of the campaign.
Lambert said: "I just had chat with him at half-time. It is easy go in and absolutely take the paint off the wall. I knew that wouldn't do him any good.
"I thought he responded brilliantly in the second half. He didn't let it affect him, which was great and he has been excellent for me this season.
"But when you're playing at this level and you make mistakes with the calibre of strikers you're playing against, you know what can happen."