West Brom boss Di Matteo delighted changes paid off in derby win
He said: "The aim was to get a win and we did it and it was a good performance.
"We controlled the majority of the game and managed to score three goals in the second half.
"It was a bit disappointing the goal we conceded from a set piece - but apart from that we didn't give them any chances.
"We didn't get hold of midfield in the first half. It is a bit of a risky move because you are 1-0 down and we removed a striker.
"But I felt I had to get another midfielder on but I put Peter up front and it worked. It doesn't always come off. It's the players who have to perform and they did brilliantly in the second half.
"Peter was a threat, a good outlet, but it was not just him. The whole team stepped it up in the second half."