Shakespeare said: "When you make a substitution you always want an instant impact and they don't come much quicker than Paul's equaliser."
Shakespeare also revealed on-loan Manchester United starlet Tom Cleverley is likely to miss making his England U20s debut after he suffered a suspected dislocated shoulder.
Shakespeare added: "He has suffered a shoulder injury, a suspected dislocation and has gone to hospital. We're just waiting to know how serious it is but it is a huge disappointment because he could now miss making his England debut."
"We weren't at our best. We didn't pass the ball well and said at half-time that we have to compete more and play at the higher tempo, which we did."