Second seed Hubert Hurkacz was a shock second-round casualty from the Citi Open on Wednesday after a straight-sets defeat to Emil Ruusuvuori.
World number 46 Ruusuvuori triumphed 6-4 7-6 (7-3) in one hour and 43 minutes to book a quarter-final spot.
Hurkacz, who is ranked 11th in the world and reached last year's Wimbledon semi-finals, fought hard but failed to capitalise on four break points throughout the match.
"He had an early break point, but then I was able to keep that service game and give myself a chance to break him and I was able to use it and then just try to keep my own serve," Ruusuvuori said.
"I just tried to hang in there and tried to stay as tough as [I] can."
Wimbledon runner-up Nick Kyrgios defeated 14th seed Tommy Paul 6-3 6-4 in one hour and 25 minutes.
The Australian hit 29-21 winners, with the majority coming from his serve and forehand, sending down 15 aces, winning 84 per cent on his first serve.
Kyrgios, who broke Paul in his opening service game, converted three of four break points for the match, while the American failed to capitalise on any of his four.
Sixth seed Denis Shapovalov was bundled out in the second round by American wildcard J.J. Wolf 6-2 6-7 (5-7) 6-3 in a major upset.
Third seed Taylor Fritz avoided an early exit with a 6-4 6-4 win over Australian Alexei Popyrin in one hour and 11 minutes, while fourth seed Reilly Opelka came from a set down to defeat Denis Kudla 6-7 (6-8) 6-4 6-4 in just over two hours. Opelka sent down 28 aces across the match.
Fifth seed Grigor Dimitrov got past Adrian Mannarino 6-1 3-6 7-5 and ninth seed Holger Rune brushed off Benoit Paire 6-3 6-2.
Francis Tiafoe defeated Christopher Eubanks 6-3 7-6 (7-2), while 13th seed Maxime Cressy fought back from an early deficit to get past Jack Sock 4-6 6-4 6-0 to set up a third-round clash with top seed Andrey Rublev.
There were defeats for 11th seed Alex de Minaur to Yoshihito Nishioka 3-6 7-6 (8-6) 6-2, 12th seed Sebastian Baez against Sebastian Korda 6-1 6-4 and 15th seed Aslan Karatsev against Andy Murray's first-round conqueror Mikael Ymer 6-4 3-6 6-4.
At the Los Cabos Open in Mexico, second seed Felix Auger-Aliassime had no troubles against local Juan Alejandro Hernandez Serrano, winning 6-3 7-5.
American sixth seed Brandon Nakashima also progressed into the quarter-finals with a 6-3 6-3 win over Max Purcell, while Miomir Kecmanovic beat Jordan Thompson 6-4 6-2.
Nadal unsure of future involvements after Laver Cup withdrawal
Rafael Nadal says he cannot commit himself to future tournaments after his withdrawal from the Laver Cup.
Nadal shared news on Thursday that he would not make an appearance at the annual event in Berlin, stating that it would not be in the best interests of Team Europe if he were to participate.
The Spaniard was last in action playing doubles at the Paris Olympics with Carlos Alcaraz, and while he says he is in a good space mentally, he was not able to confirm when he would next make a professional appearance on a tennis court.
He said: "Mentally, I’m good, no problems. I'm at home enjoying other things, training as much as I can every day.
"No drama, obviously these are decisions [the Laver Cup withdrawal] that are being made, and this was a possibility - it's been a while without competing. There will be someone else who can do better.
"Right now I’m not in a position to put myself down for anything.
"I said [I would play] until the Olympics and then we would see, and I'm in that period of rest."
Nadal has endured a difficult 2024 so far, playing just 21 competitive singles matches with a record of 13-8.
He has only one grand slam victory to his name this year, beating Jack Draper in the Australian Open, but he lost in the first round of the French Open to eventual finalist Alexander Zverev.
Alcaraz sends Spain into Davis Cup last eight
Carlos Alcaraz has led Spain to the quarter-finals of the Davis Cup Finals after a straight-sets win over Ugo Humbert.
The 21-year-old needed just one hour and 21 minutes to cruise through with a 6-3 6-3 victory, hitting 21 winners to his opponent's 14 as he backed up Roberto Bautista's win earlier on.
Bautista had to come from behind to edge past Arthur Fils, beating him 2-6 7-5 6-3, and converting 40% of his break points, bettering the Frenchman's 27%.
Spain are through in Group B, but elsewhere in Group D, US Open semi-finalist Jack Draper's return was unable to inspire Great Britain to victory.
Dan Evans was beaten by Tomas Martin Etcheverry earlier on Friday before Draper's first match since New York ended in a straight-sets 7-6 (7-4) 7-5 defeat to Francisco Cerundolo.
Despite making fewer unforced errors than the Argentinian (23 to 39), the British number one struggled to find an edge, though Evans and Neal Skupski claimed a consolation win in the doubles to make it 2-1.
They sit second in the group, missing the chance to qualify for the last eight, and now needing a win against Canada, who have been in fine form so far.
Auger-Aliassime and Shapovalov sweep aside Finland at Davis Cup
Felix Auger-Aliassime and Denis Shapovalov moved Canada to the brink of qualification in the Davis Cup Finals group stage, comfortably dispatching Finland in Manchester.
Shapovalov needed just an hour and 13 minutes to beat Eero Vasa 7-6 (7-2) 6-2, backing up his win against Argentine Francisco Cerundolo on Tuesday.
The Canadian served five aces to his opponents' three, producing three love games in the final set to get his nation off to a flying start.
Auger-Aliassime followed up Shapovalov's victory with another straight sets win, this time over Otto Virtanen, emerging a 6-2 6-3 victor.
The world number 21 was dominant on serve throughout his 73-minute triumph, saving all three break points he faced and winning 86% of his first-serve points.
Auger-Aliassime and Shapovalov then prevailed in the doubles against Harri Heliovaara and Virtanen in another straight sets win, putting them top of Group D without dropping a set against their opponents.
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