Pietersen made 113 runs to help England close day three of the third Test on < ahref="/cricket/england/ashes/news/england-dig-in-on-day-three_96589.html">297-7, and Willis believes that the South Arica-born batsman is a unique talent.
"Pietersen is a very special member of this England side," Willis told Sky Sports News.
"He has got class that the others don't have. Pietersen can turn a match in the space of half an hour.
"It was a tantalising battle, but it is a surprise Pietersen hasn't scored 100 before [at Old Trafford] because it's a cracking batting pitch."
Willis is England's second all-time wicket taker in Test matches, having claimed 325 dismissals in 90 Test matches between 1971 and 1984.