Adrian Lewis and Raymond van Barneveld are the only two players who managed to hit two nine-dart finishes at the World Championship. 'Jackpot' even hit one of his two perfect legs against 'Barney', the other one was in the 2011 World Championship final.
Lewis also won that final to win his first world title. Four years later, he hit his second nine-darter against Van Barneveld in the third round of the 2015 edition. However, the Dutchman won this game 4-3 in sets, meaning Lewis did not really enjoy his perfect leg this time.
https://www.youtube.com/watch?v=aC33Tg0dwTg
https://www.youtube.com/watch?v=wOHMm6UkgF8