What Would You Do?: Expecting One Concerto And The Orchestra Begins Playing Another

I just came across an article about a concert which took place some years ago where concert pianist Maria Joao Pires came to a free open concert in Amsterdam expecting to play one Mozart concerto and the orchestra began playing an entirely different concerto.  She was horrified and the shock on her face is telling.  She takes a step back after having a brief chat with the conductor (all while the orchestra is playing) and digs into her memory banks and begins playing the concerto along with the orchestra.  A true triumph of the mind and spirit. 

Here's The Telegraph article about it and the video as well: