The two teams meet in the Capital One Cup fourth round with a quarter-final match at home with Chelsea awaiting the winner.
Poyet admits he has been impressed and surprised by Southampton's start to the Premier League season - Pochettino's men are sixth and have conceded just four goals.
He said: "They have done very well. They have kept the core of the team. They have added two or three players who are performing at great levels, so they are a very strong team.
"They are the biggest surprise so far, but it's totally deserved because they play a football which is quite brave and very aggressive, especially pressing at the beginning of the game, so there are plenty of things we need to do right to win this tie."
Poyet will be forced to make at least two changes for the game with midfielder Lee Cattermole and full-back Andrea Dossena having both been sent off in a calamitous first half against Hull.
It was the seventh red card of Cattermole's Premier League career and while Poyet felt it was harsh - Sunderland have decided not to launch an appeal against either decision - the manager admits he will have to work hard with the midfielder.
He said: "In any team, you have got different characters and you need to, as a manager, use them to the best of their ability knowing they can do one thing or another, or they can make this mistake or another.
"Lee, we know that when he is frustrated he is maybe going to make this kind of tackle.
"Many managers have talked about him. Me, I am going to try to manage him my way.
"I respect other opinions but I am going to do it my way with him internally, and we will see if he improves that reputation that he has got at the moment in England that he cannot make a tackle."