The Championship promotion favourites suffered a 3-1 loss at Elland Road on their first outing of the 2018-19 campaign.
Goals from Mateusz Klich, Pablo Hernandez and Liam Cooper were enough to give Leeds boss Marcelo Bielsa a dream start, while condemning Rowett to defeat in his maiden match since jumping ship from Derby County.
Rowett was particularly unhappy with the nature of his side's defending in West Yorkshire, and admits that there is plenty to work on before facing early pacesetters Brentford next weekend.
"It wasn't the result we wanted nor the performance we wanted," he told reporters after the match. "It was something we warned the players about, settling down quickly and adjusting to a different style of football, and we didn't do that today.
"Leeds looked as though they had more intensity and more aggression about them today, and I also felt for vast parts of the game, our basic defending as a team was very, very poor. What you do hope is that the players with Premier League quality show that throughout the game, but I don't think enough of them did that today.
"Tom Ince looked very bright, James McClean worked incredibly hard and I was happy for Benik [Afobe] to get his first goal, but after those I think a lot of the guys were surprised by the intensity of the game.
"You would have to ask the players that themselves, but from the sidelines that is what it looked like to me. "It was a real kick up the backside today, and we have a lot of work to do, but we will keep working incredibly hard and we will get there."
Rowett has brought in six new players prior to the transfer window closing on Thursday.