If there was one noteworthy thing about Everton's routine 3-0 friendly win over Dutch side FC Twente on Wednesday it was how the pair looked to link up every time they got the ball after joining the fray in the second half of the game.
Everton boss Ronald Koeman will be hoping that it represents the start of a fledgling partnership between the pair and Dutchman Klaassen was full of praise for his new team-mate after the game.
"It is great to combine with Wayne," said Klaassen. "He is a quick thinker and I like that. He looks for me when I make my runs into the area."
"Did he know me? I think he did! He played against Ajax in the Europa League final in May. He knew quite a bit about Ajax."
"Also, it's not as if I am a young boy who has only just joined on to the big stage. I played plenty of matches for Ajax and won league titles. It's nice he knows that."
"It is not all that difficult to combine with Wayne. He is a world class striker who has joined us and is playing in front of me. I thought that it was great he came to play for Everton. I was delighted when I heard the news that he was coming back."
The former Ajax man also backed-up Rooney's assertions that he had not joined Everton to wind down or move to a 'retirement home as he put it', saying: "But he isn't coming back to wind it down or take it easy. You can see it in him - he is really fit still. He is hungry on the pitch and he wants to be at a club with a big ambition. He came here for the reasons I did, to be successful."
It will certainly be interesting to see how the pair dovetail on the pitch this coming season.