The Well boss declared that the English keeper pulled off world-class saves to keep his side out at Parkhead.
"He's certainly pulling off world-class saves - the one he pulled off today was unbelievable," he told BBC Sport.
"One goal with five minutes to go and who knows? You then put pressure on and the crowd get edgy."
McCall went on to concede that his players were guilty of paying Celtic too much respect during the Scottish Premiership clash.
"Once we grew into the game I was fairly happy, but both goals are poor from our point of view," he McCall. "We gave them a little bit too much respect."
The result sees Celtic move to the top of the table, while Motherwell remain in third.