The Gunners reject capped his performance by teeing up Peter Odemwingie for the opener before firing his first goal of the campaign in the 73rd minute as Albion inflicted Arsenal to their first defeat in all competitions this term.
"Jerome has had a full pre-season," said Di Matteo.
"He's started the season in good form and good shape. He had a very good game today but it was a collective good performance.
"I had a lot of players on the pitch today who performed at a high level. He missed Wednesday's game with a groin problem but he was very keen to play today.
"I don't think he needed to prove a point.
"We were just fired up to play a good game and put in a good performance."