Fifteen-year-old Cori "Coco" Gauff clinched one of the great Wimbledon upsets as she defeated five-time champion Venus Williams on the opening day on Court One. Gauff is the youngest woman to qualify for the tournament in the Open era but she played like a veteran, outplaying a veteran of these courts to snatch the first set, and after Williams saved three match points, she was finally beaten in straight sets 6-4 6-4. Aged 39, Williams is considered Wimbledon royalty as she has been part of the All England Club family for over two decades, having won the singles title five times – including two before Gauff was even born. But Gauff produced a flawless performance in one hour and 19 minutes, and she told the BBC: "I don't really know how to deal with it – that's the first time I cried after a match, winning. I don't know how to explain this feeling. " I definitely had to tell myself to stay calm as I've never played in front of such a big crowd. I kept telling myself that the lines and the court size is just the same as where I always play. " "I told Venus after the match 'thank you' – I wouldn't be here if it wasn't for her." Guaff, the youngest player to qualify for the main draw in the professional era, was in no mood to play a lady-in-waiting as she made a mockery of the 24-year-age difference and 269 ranking spots that separate her from Williams. The roar from the crowd was deafening as the teenager broke Williams in the fifth game of the first set, when a backhand from her opponent went long. Williams recovered from a break down in the second, but Guaff instantly responded in the ninth game as she broke the seven-time Grand Slam champion for a third time. Gauff – who wasn't even born when Williams had claimed four of those titles – secured the victory on serve to the delight of her parents in the box. "I wouldn't say I didn't expect to win the match. I knew that I was going to go out there and play the way I play," the youngster added. "I wasn't surprised that I won. I mean, I was just overwhelmed at the end." Madison Keys, seeded 17th, made short work of Thailand's Luksika Kumkhum winning 6-3 6-2 to reach the second round while Elina Svitolina handed Australia's Daria Gavrilova a bagel en route to a 7-5 6-0 victory. Former US Open finalist Keys was the first player through to the second round with a performance that illustrated her 17th seeding. Third seed Karolina Pliskova bludgeoned her way into the second round of Wimbledon on Monday, using her huge serve and searing forehand to fend off tenacious Chinese challenger Zhu Lin 6-2 7-6(4). She zipped through the first set, whipping a crosscourt return into the corner to wrap it up in 27 minutes. But, as Zhu found her feet and her range on the new grass, the 27-year-old Czech began to look a little out of sorts and produced a few loose shots among 18 unforced errors. Zhu, 25, who failed to qualify for Wimbledon the last three years, scurried up and down the baseline, chasing everything down and countering the serve with some fine returning. Pliskova had to use that booming forehand to get her out of trouble in the 12th game of the second set, saving three set points in a marathon game of seven deuces. That game ended Zhu's resistance and Pliskova, a former number one, who could rise to the top spot again at the Championships, took the tiebreak and the match after 1 hour 21 minutes. Meanwhile, French Open runner-up Marketa Vondrousova was 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. 27th seed Sofia Kenin overcame Astra Shami 6-4 6-2, but 2018 Wimbledon quarter-finalist Camila Giorgi suffered a 6-3 6-3 defeat to Dayana Yastremska.