Foster kept United at bay in the first half, making a superb save to deny Ashley Young.
Not that Clarke was surprised at such heroics.
"Ben Foster made some good saves," said Clarke. "That's why we spent our whole transfer budget on Ben in the summer."
After a difficult first half, the visitors came to life after the break, triggering United into a tactical change, with Chris Smalling dropping into central defence alongside outstanding skipper Nemanja Vidic and Chris Smalling following Robin van Persie's introduction.
"It is not demoralising," said Clarke of Van Persie's introduction. "The fact they had to bring some of their big guns off the bench shows how well we were doing.
"In the first we were too timid. We spoke at half-time about being too respectful and in the end, the scoreline doesn't reflect the way we played."