Mateta struck twice for the 2-0 win at London stadium.
“Of course it's always most important for a striker to score,” Glasner said. “It's his most important job to do for the team.
“In the first-half I think we controlled the game but we didn't create many chances – also West Ham defended their box pretty well – but in the second-half we were talking about overloading and finding good positions, and there's a build-up from the back and it starts and when Ebs (Eze) gets the ball, he's completely free because he's moving into the free space, and then he can make pressure on the defence, and then JP is always running.
“It was a little bit similar at Leicester – it was Ismaïla Sarr getting the ball in this area, making pressure and finding the right moment for the pass, and this is what we're always training and talking to them about, and then when JP gets the ball and having a free finish somewhere around the box, it's very often a goal.
“It was an important goal, but he also worked hard like all the others today in our defensive shape, and it's the third win in a row, the third clean sheet in a row, so I'm really delighted.”