According to Official Guinness Records,
The best ever performance by a wildcard entrant at the Wimbledon Championships is that of Croatian Goran Ivanisevic in 2001. Invited to play in the competition by the All England Club, Ivanisevic, ranked 125th in the world won the Men's singles title by beating Pat Rafter (Australia) 6-3 3-6 6-3 2-6 9-7 in the final and becoming the first wild card entrant to win a Grand Slam tournament. The Croatian's popular win came in his fourth final appearance and he also served a record 213 aces, including 27 in the final, throughout the tournament.
For a complete list of 2001 records, please visit 2001 Guinness Records in United Kingdom.