Belinda Bencic said it was an “amazing feeling” after she beat 2017 runner-up Venus Williams in the first round of the Australian Open.
The unseeded 20-year-old Swiss, ranked 78th, won 6-3 7-5 on the opening day in Melbourne.
She reached the top 10 as an 18-year-old but a wrist injury led her to drop to 318 in the rankings in November.
Bencic has now won 16 tour matches in a row, and 28 of her last 31, as she races back up the rankings.
“It means so much to me,” she said.
“I lost to Venus four times and I tried my best to give my all today, and changed some things tactically.
“I think it was a huge opportunity and I used it, so I was very relived after the match point. After the injury and the tough times it’s really an amazing feeling.”
The match had been widely viewed as the pick of the first-round draw, with Bencic’s lowly ranking no indication of the threat she posed to fifth seed and seven-times Grand Slam champion Williams.
Venus Williams reached the finals of the Australian Open and Wimbledon in 2017, as well as the last four of the US Open
Meanwhile, Kyle Edmund claimed the best win of his career as he knocked out 11th seed Kevin Anderson in five sets at the Australian Open.
Edmund, the only British man in the singles draw, won 6-7 (4-7) 6-3 3-6 6-3 6-4 in the first round in Melbourne.
The 23-year-old, ranked 49th, twice came back from a set down and recovered from 2-0 behind in the final set to win in a minute short of four hours.
He goes on to face Uzbekistan’s Denis Istomin in the second round.
Edmund’s best previous victory at a Grand Slam tournament in, terms of rankings, had been his win over 15th seed Richard Gasquet at the 2016 US Open.
He had lost his only previous encounter with Anderson over five sets at last year’s French Open, and he was in no mood to suffer a similar defeat
US Open finalist Anderson, 31, was predictably dominant for periods on serve, using his 6ft 8in frame to good effect as he finished with 35 aces to Edmund’s 11.
Edmund had been working on his returns in the off-season, however, and it paid off.