Southampton moved second in the top flight on Saturday with a 1-0 win over Mark Hughes' side at St Mary's Stadium and the sides will lock horns again on Wednesday at the Britannia Stadium.
Sadio Mane scored the only goal of the game at the weekend and Koeman revealed he will not make wholesale changes for their cup clash.
The Dutchman - who has enjoyed a hugely positive start to life in England - feels the competition is one his side can be a force in.
"Maybe people are not surprised any more about our performances and our qualities but it's nice to look at the table and it's nice to enjoy the Sunday," he explained.
"But on Monday we start again to prepare ourselves for Wednesday.
"It's great for the fans to see Southampton up in the [table] and we're enjoying it but we know that we have to work hard. We showed that.
"We will prepare ourselves in the best way because we would like to win something."
With no fresh injury concerns to worry about ahead of the League Cup tie, Koeman also stated his intention to name a strong XI, as he did for wins over Millwall and Arsenal in previous rounds.
"Maybe if there are some injuries or some physical problems then we will have to change," he added.
"What I did in the first two or three games of the League Cup [was] we changed a maximum of three positions.
"We don't have that quality to change eight or nine positions because the group is not big like in the big teams.
"I don't like that. I like rotation but I don't like to change everybody."
