no body expected mamluks to win.... they were not known for military strength or any significant victories..
Actually, the Mamluks were known very well to be extremely fierce and skillful warriors. Infact, their whole lives revolved around warfare. The reason why no one expected them to win was 1) the perceived Mongol invincibility and 2) the tumultuous political landscape of the infant Mamluk Sultanate. The first thing they were known for and still are remembered for is their military prowess.