Opelka fired 23 aces and 59 winners and goes on to face 2016 runner-up Milos Raonic of Canada.
Reigning champion Djokovic was never really threatened by American Kudla as he strolled to a 6-3 6-2 6-2 win on Centre Court. The American reached the fourth round here in 2015 and recorded his lone ATP 500 semi-final a year ago at the NOVENTI OPEN.Anderson's dominant opening-round win over Frenchman Pierre-Hugues Herbert proved he's fully recovered from the right elbow injury that has limited him to three tournaments since the Australian Open.
"There were some moments in the match where maybe I could have done better", Djokovic said.
For Opelka, a 21-year-old who is measured at an inch short of seven foot, it was a first main-round draw win at Wimbledon and just his second ever grand slam win.
Also, No. 10-seeded Karen Khachanov of Russian Federation advanced by beating Feliciano Lopez 4-6, 6-4, 7-5, 6-4 on No. 1 Court.
Sakkari, the 31st seed, will now take on world number eight Elina Svitolina of Ukraine in the third round on Friday. A trainer attended to Gasparyan, and Svitolina came over to check on her opponent, bringing her a bottle of water.
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Svitolina, on the other hand, was two points from losing to Margarita Gasparyan in the second set but eventually won when her opponent retired with an injury at 5-7, 6-5. "So it's important just to drink lots of fluids", Svitolina said.
Former world number one and double Australian Open victor Victoria Azarenka swept past Australia's Ajla Tomljanovic 6-2, 6-0.
"It's going to be a big challenge for me, a tough one, because she's playing not very flat but she's very aggressive".
The American schoolgirl is the youngest player in the last 32 since Jennifer Capriati, also 15, went all the way to the semi-finals 28 years ago.
Belgium's David Goffin advanced with a routine 6-2 6-4 6-3 victory over Jeremy Chardy while Czech Jiri Vesely joined him in the third round by beating Pablo Cuevas 4-6 7-6 (7-5) 6-4 6-4.
Gauff beat five-time champion Venus Williams in the first round.