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 told BBC Radio 5 live.
“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.
Bencic, watched in her player box by Roger Federer’s parents, grabbed the first break but Williams hit back after a rain delay resulted in the roof being brought across on Rod Laver Arena.
The Swiss continued to press, however, breaking once more to clinch the set and pegging Williams back twice at the start of the second.
Williams held on under huge pressure to make it 4-4 but Bencic sealed victory after one hour and 55 minutes.
“I changed the perspective a little bit and I came back now appreciating more being on the tour and just playing matches,” added Bencic.
“That is something I learned and I want to keep – my fun and motivation, even though it’s so much hype and so much pressure sometimes.”
With defending champion Serena Williams absent following the birth of her first child, it is only the third time in 20 years that neither Williams sister has reached the second round at a Grand Slam.
“I think she played well,” Venus Williams said.
“I don’t think I played a bad match. She just played above and beyond. I just have to give her credit for that.”