China's Wang Xinyu stuns Pegula in Wimbledon second round
The American, ranked fifth in the world, battled back after losing the first set, saving a match point in the second-set tie-break, before levelling the match.
But China's 42nd-ranked Wang raced into a 5-0 lead in the decider before wrapping up the contest to record her first win against a top-10 player.
Wang, 22, said: "Couple of days ago I was asking my coach, 'When will this happen?'
"Jessica was really tough to play on grass. Her ball was super low and I'm just really happy I won in the end."
Wang will face Britain's Harriet Dart, who defeated Nottingham champion Katie Boulter, for a spot in the last 16.
Defending Wimbledon champion Marketa Vondrousova earlier this week became the first defending women's champion to lose in the first round for 30 years