Di Matteo said: "It was hard work. At the end, the result may have looked comfortable but it was a hard game for us.
"Plymouth came out of the blocks really well and we had to change a few things around.
"But getting the equaliser and a second goal before half-time was important and we were better in the second-half.
"We are top of the league and we will enjoy that. We are also still unbeaten and we will enjoy that as well.
"We have our philosophy of how we want to play and we can score from anywhere in the team, which is important.
"We are going in the right direction and I think the chairman is very happy that we are unbeaten."
While Albion are top of the table and flying, Plymouth boss Paul Sturrock was left downcast after again seeing his side undone by a poor defensive display.
Plymouth are without a win this season and have collected only two points from a possible 18.
Sturrock, whose side changed their strip at half-time from white to green after struggling to pick each other out, said: "Until we lost the second goal we did very well.
"I am going to use a phrase I have used for the last six games and that is, 'if only'.
"But we can't keep saying, 'if only'. We are losing bad goals and Paul Sturrock prides himself that his teams are normally hard to score against.
"The first goal came from a corner and we spent 45 minutes working on defending them in training on Friday and my worry now is that it is playing on the minds of the players.
"We have lost too many from set-pieces. We just need a wee break because at 2-1 down we hit the bar.
"The important thing for us is that we get just three points from somewhere even if it is with the worst performance of our lives and the ball goes in off someone's backside. That is all I want."