Cori Gauff overcame a 24-year age gap to stun Venus Williams on her Wimbledon debut.
The 15-year-old American is the youngest woman to qualify for the tournament in the Open era but she played like a veteran in a superb 6-4 6-4 victory.
Gauff served superbly, being broken only once, and showed tremendous composure in her first main draw match at a grand slam, making just eight unforced errors compared to 25 for her 39-year-old opponent.
Williams won two of her five Wimbledon singles titles before Gauff was born and this was only the second time she has been beaten in the first round since her debut in 1997.
While Williams has been setting records at one end of the age scale, Gauff has been breaking them at the other, reaching her first junior slam final at the US Open aged just 13.
She won the French Open title last year and, on this evidence, she is more than ready to make a big impression in the senior game.
Gauff was inspired to pick up a racket by the Williams sisters and for Venus it must have been like facing a teenage version of herself as her opponent fired down serves over 110mph and scampered around the court with her long levers.
Gauff is already a terrific athlete and Williams was simply unable to hit through her. What was most impressive, though, was the way she constructed points, playing close to the lines but rarely too close and using angles to open up the court.
A break for 3-2 set her on the way to the first set without facing a break point and, when Williams double-faulted twice in a row, Gauff, who sat an online science exam at 11pm before her final qualifying match, moved 3-2 ahead in the second.
She seemed to feel the occasion for the first time serving at 4-3, double-faulting to hand back the break, but she forced another break of the Williams serve in the next game to leave herself serving for the match.
A tense game saw Williams save three match points before creating one break point, which Gauff saved with a 108mph second serve. When her fourth opportunity came, the teenager took it, then dropped to the court in disbelief.
Meanwhile, Yulia Putintseva claimed a second straight victory over Naomi Osaka to dump the second seed out of Wimbledon on the opening day.
Osaka's last match before arriving at the All England Club was a straight-sets loss to Putintseva at the Nature Valley Classic in Birmingham and again the Kazakh proved too consistent.
Osaka led by an early break but could not hold onto her advantage and Putintseva celebrated a 7-6 (7-4) 6-2 victory and one of the biggest successes of her career.
The Kazakh benefited from a crucial slice of luck at 2-2 and break point when a mis-hit backhand was shown just to have caught the edge of the line for a winner.
Osaka turned away in frustration while Putintseva fist-pumped her way back to her chair.
Osaka had a chance to break straight back but placed a straight-forward volley wide, and that proved to be the beginning of the end. When Osaka dumped a final backhand into the net for a 37th unforced error, Putintseva pumped her fist and then looked around Centre Court in disbelief.
An emotional Osaka then walked out of her press conference.
It was clear how disappointed Osaka was by the defeat as she spoke barely louder than a whisper in her post-match press conference and gave very brief answers.
The 21-year-old has not reached the final of any tournament since winning her second successive grand-slam title at the Australian Open in January and climbing to world number one.
Handling the extra attention and pressure has been a big challenge and, asked how she has picked herself up in the past, Osaka said: "The key for me was just having fun, I guess, kind of taking pressure off myself. I hope I can somehow find a way to do that."
After contemplating answering the next question about how difficult it has been to adjust to her new level of fame, Osaka turned to the moderator and said: "Can I leave? I feel like I'm about to cry," before walking out.
French Open runner-up Marketa Vondrousova was also knocked out in the first round, the Czech 16th seed beaten 6-4 6-4 by American Madison Brengle.
A few days after turning 20, the left-hander struggled to get to grips with her opponent's game as she lost in the first round for the third successive year.
Last month Vondrousova fell just short of becoming the first Czech woman to win the French Open for 38 years when she lost to Australia's Ash Barty in the Roland Garros final.
Seventh seed Simona Halep was given a tough battle by Belarusian Aliaksandra Sasnovich before battling to a 6-4 7-5 victory.
Halep, who has made the quarter-finals twice and the semi-finals once, trailed 5-2 in the second set and had to save a set point at 5-4 before sealing victory with a run of five games in a row.
