Having lost a host of key players in the close-season as well as manager Mauricio Pochettino, Southampton have emerged as the surprise package in the top flight in 2014-15.
With just two league defeats from eight, Koeman's side sit third going into Saturday's clash with Stoke City following last weekend's 8-0 rout of Sunderland.
While the former Feyenoord coach believes opponents are now well aware of threat his side can pose, Koeman also suggested his back line have yet to receive adequate praise for boasting the best goals-against column (five) in the Premier League.
Asked if the element of surprise had been lost, he responded: "Maybe, of course everyone knows after eight games the quality of Southampton.
"They know we score a lot of goals and if you make it an open game [for us] and try [to] attack then we will get a lot of space and it can be a problem for opponents.
"It's up to them, for the manager of Stoke it is his decision how they will come and what they plan. We will prepare ourselves how we like to play at home - trying to play attractive football and score goals.
"We scored a lot of goals but only [conceded] five, which is another quality to win games.
"A good defence is important, clean sheets are important. It's the whole organisation because defending starts in front and we like to press.
"It's not possible all game but we have to wait for the good moments to press. All that makes a good organisation."
Koeman - who dismissed rumours regarding a potential swoop for Dirk Kuyt - warned his side not to get carried away by their convincing win at the weekend.
With Stoke losing just once on the road in the Premier League this season, Koeman does not feel Southampton are good enough to take opponents lightly.
"We have to continue because we don't have enough quality to play at 80 per cent, we have to play every game at 100 per cent then we can be successful," he added.
"Of course the [8-0] result brings a lot of attention but the players are fantastic. Already after the [Sunderland] game they spoke about next week.
"They had two days off and, starting on Wednesday, we showed the players clips from the first 20 minutes [against Sunderland].
"It was not the way we like to start the game at home. We showed them everything but they know exactly what happened, it wasn't a good start to the game.
"We can start much better than we did last weekend."
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