The five time US Open champion was given the loudest cheer at the Arthur Ashe stadium.
The 6-2, 2-6, 6-3 win at the Pat Rafter arena was the 25-year-old's first in four attempts against world number five Nishikori and will boost his confidence ahead of the Australian Open, which starts on January 16 in Melbourne.
Fourth seed Grigor Dimitrov survived a scare against Pierre-Hugues Herbert before holding his nerve to win 3-6, 6-2, 6-4 in the second round of the Monte Carlo Masters on Tuesday, while Dominic Thiem edged out Russian youngster Andrey Rublev.
The Adria Tour tournament, was the brainchild of World No 1 Novak Djokovic, who, along with his wife also tested positive for COVID-19 after the Adria Tour's second leg in Croatia.
A battle-scarred Rafa Nadal admitted he got lucky as he moved into the semi-finals of the Australian Open on Wednesday with a 3-6, 7-6 (3), 7-6 (7), 6-2 win over Bulgaria's Grigor Dimitrov.
Rangy 19-year-old Mensik, the 2022 boy's singles finalist at Melbourne Park, sealed the match in style with a searing forehand winner to push the three-times Grand Slam finalist and sixth seed to the exit.
Novak Djokovic fights past Aleksandar Kovacevic to reach the last 16 at Indian Wells Open, setting up a clash with defending champion Jack Draper.
Dimitrov has enjoyed the best season of his career in 2017, clinching four titles overall, including his first Masters title in Cincinnati.
Electronic line calling systems were also affected by the power cut, the ATP said, while spectators shared pictures of dark hallways at the Manzanares Park Tennis Center.
World No 1 Rafael Nadal defied a painful blister and the dogged challenge of Grigor Dimitrov to reach the semi-final of the Australian Open on Wednesday.
Novak Djokovic was dumped out of the Madrid Open in the second round on Tuesday when he went over on his ankle and incurred the wrath of the locals on the way to a shock 7-6, 6-7, 6-3 reverse to Bulgarian Grigor Dimitrov.
Bulgarian Grigor Dimitrov smashed three rackets on his way to losing the Istanbul Open final to Argentine Diego Schwartzman on Sunday.
Roger Federer ended Grigor Dimitrov's seven-match winning streak and showed the Bulgarian he has some way to go to live up to his 'Baby Federer' tag with a 6-3 7-6 (2) quarter-final victory at the Basel Open on Friday.
Novak Djokovic reached the Paris Masters final for the sixth time
Bulgaria's Grigor Dimitrov edged out South Africa's Kevin Anderson 7-6 (7-1), 3-6, 7-6 (7-5) in a three-hour slugfest to claim his second career title with victory in the Acapulco International final on Sunday.
Bulgarian's Grigor Dimitrov claimed a first career win over former world number one Rafael Nadal at the eighth time of asking to reach the semi-finals of the China Open on Friday.
The 26-year-old has not always handled the expectations placed on his shoulders after he won the Wimbledon junior title in 2008 with a game style uncannily like Federer's.
Grigor Dimitrov stood one win away from the biggest title of his career on Saturday after ending his Jack Sock jinx to reach the final of the season-ending ATP Finals at the 02 Arena.
Eight-times champion Rafael Nadal was taken to the brink by Bulgarian Grigor Dimitrov before completing a 6-2, 2-6, 6-4 victory on Friday to reach the Monte Carlo Masters semi-finals. He will meet Frenchman Jo-Wilfried Tsonga, who beat Swiss Stanislas Wawrinka.
American Mardy Fish and Bulgaria's Grigor Dimitrov had to be separated by the match referee when they squared up to each other during a changeover in a bad-tempered Hopman Cup encounter on Friday.
Top seed Carlos Alcaraz reached the semi-finals at the Queen's Club Championships with a straight sets victory over Bulgarian Grigor Dimitrov.
Defending champion Federer, battling a flu bug according to the local media, was made to work hard by his Bulgarian opponent before the Swiss master prevailed 6-4, 6-7(4), 6-4 at the Pat Rafter Arena. "It was tough. Grigor's a great shotmaker, the future's ahead of him in the game," Federer said after setting up a semi-final against Austrian youngster Dominic Thiem.
Defending champion Andy Murray was beaten 6-1, 7-6(4), 6-2 by Bulgarian Grigor Dimitrov in the quarter-finals of Wimbledon on Wednesday.
Dimitrov was showing signs of fatigue from his three-hour third-round match earlier in the week and could do little to stop the Spanish world number three, who next faces Argentine Francisco Cerundolo.
Edmund, playing in his first Grand Glam quarter-final, showed no nerves as he blazed away with his fearsome forehand to subdue a nervy Dimitrov.
Earlier in the day, Croatia's Borna Coric said he has tested positive for coronavirus. He became the second player to test positive for COVID-19 after Bulgaria's Grigor Dimitrov.
Serena Williams creates ripples with her latest outfit.
A patient Roger Federer weathered a second set storm from Grigor Dimitrov before slapping down the Bulgarian challenger 6-4, 3-6, 6-1, 6-4 to reach the fourth round of the Australian Open and clinch his 300th win in Grand Slams.
Novak Djokovic is one win away from a 100th career singles title after breezing past Grigor Dimitrov 6-2, 6-3 on Friday to reach the Miami Open final, where he will face either third seed Taylor Fritz or rising Czech Jakub Mensik.
Argentine Juan Martin del Potro is determined to go one step further than his runner-up finish 12 months ago at the World Indoor Tournament as he reached the final with a 6-4, 6-4 win over Bulgaria's Grigor Dimitrov on Saturday.
Seven-times champion Novak Djokovic scored his 100th match win at Wimbledon and led the march of the old guard into the last 16 on Saturday while an ailing Barbora Krejcikova's title defence ended in defeat and tears.
Andy Murray has set up a mouth-watering clash with Grigor Dimitrov and a chance to avenge his defeat at Wimbledon after hammering Portugal's Joao Sousa 6-1, 6-1, 7-5 to reach the fourth round of the Australian Open in Melbourne, on Friday.
Marin Cilic had never beaten a Top-5 player on grass in his entire career before Thursday.
Photos from the Queen's Club tennis tournament played in London on Monday
Philippine wildcard Alexandra Eala pulled off the biggest win of her young career with a stunning upset of Polish world number two Iga Swiatek.
World No 30 has Monfils stepped in to replace injured Fabien Reboul
Images from all the action on Day 9 at the Australian Open in Melbourne on Wednesday
Goran Ivanisevic, Djokovic's coach, was greeted with jeers from fans when he broke the news courtside.
Bulgaria's Grigor Dimitrov upset top seed and defending champion Milos Raonic of Canada at the Brisbane International on Saturday to set up a title clash against Japan's Kei Nishikori.
Bulgarian Grigor Dimitrov kept cool in the Rod Laver Arena maelstrom to knock home favourite Nick Kyrgios out of the Australian Open in a fourth-round thriller on Sunday.
