Yesterday, the London Mayor accepted Ms Middleton's offer after she said she would like to see whether the Middleton or Johnson family was the most competitive.
Writing in The Spectator, about her recent disappointment when an avalanche prevented her from completing a endurance ski challenge, the Duchess of Cambridge's younger sister said:
In response, Mr Johnson said he was "game" in a tweet to the Spectator's editor Fraser Nelson:
Today, during a visit to Ealing studios, after announcing a £750,000 investment in London's TV and film industry, Mr Johnson said:
"I feel very nervous clearly because she seems to be very good. Well, she claims to be very good.
"But I'm very happy to do this because it's a chance to promote what we're doing with sports legacy London. If Pippa's kind offer can be used to promote that then I'm all for it."
He then seemed to confuse Ms Middleton with her sister the Duchess of Cambridge, and asked himself: "Pippa Middleton. She's a duchess is she? Or isn't she just a sister of a duchess?"
A table tennis club in Holborn has warned Mr Johnson to watch out for Pippa Middleton's skills at the table.
The mayor famously told the story of the origins of table tennis -or 'wiff-waff' when he accepted the Olympic flag on behalf of London at the end of the Beijing Olympics in 2008.
The mayor said that ping pong was invented on the dinner tables of England and was known as 'wiff-waff'.
He will be hoping that he fares better than the Prime Minister did when he teamed up with US President Barack Obama two years ago.