The Queen's grandson and his wife sat next to the Duchess of Cambridge's siblings as they watched a round of wheelchair rugby at the Queen Elizabeth Olympic Park in London.
The match was no ordinary one, however, as making up the teams were Prince Harry and Zara Tindall as well as former Olympic stars including Denise Lewis and Dame Kelly Holmes.
CLICK ON PHOTOS FOR FULL GALLERY
Pippa and James supported their sister's brother-in-law as he scored the game's first goal, while Peter cheered on his sister Zara, whose husband Mike Tindall was on the opposing team.
The couple, who welcomed their first child Mia Grace Tindall in January, still took the chance to steal a kiss during the fiercely competitive game.
Clearly thrilled by the night's sporting activity and by the work of his cousin Harry in putting on the four-day event, Peter tweeted a message of congratulations to those who are involved in the Invictus Games.
"Unbelievable atmosphere @InvictusLondon," he wrote. "Very proud of Harry and all the guys and girls taking part. #copperboxarena #SupportOurTroops".