Bayern remain on 49 points, with second-placed RB Leipzig, who have 44, in action at Hertha Berlin on Sunday. Fourth-placed Frankfurt are level on 42 points with VfL Wolfsburg, who are third and won 3-0 at Arminia Bielefeld on Friday.
With Germany coach Joachim Loew watching in the stands ahead of international matches in March, Younes, who won the last of five Germany caps in 2017, thundered in a shot from the edge of the box in the 31st after taking on the entire Bayern defence.
The Bavarians, who won their sixth title in less than nine months with their Club World Cup triumph last week in Qatar, looked anything but fresh and were struggling for ideas to find a way back into the game.
Bayern had a string of chances, with Frankfurt goalkeeper Kevin Trapp kept busy throughout the second half.
But Frankfurt, playing without injured top striker Andre Silva, hung on for their fifth straight league win.
Borussia Moenchengladbach’s European aspirations suffered a big blow with a 2-1 loss at Mainz 05 after Kevin Stoeger’s 86th minute winner saw them drop to eighth place on 33.
It has been a whirlwind week for Gladbach after coach Marco Rose announced he would join Borussia Dortmund next season.