Team Europe are poised to seal yet more Laver Cup glory after producing another dominant display against Team World, though the focus was on Nick Kyrgios following comments about his long-term future.

Europe swept Saturday's four matches in Boston to stand on the cusp of a fourth consecutive Laver Cup triumph – the defending champions lead 11-1 and require just two more points to clinch the title.

Stefanos Tsitsipas blitzed Team World's Kyrgios 6-3 6-4 at TD Garden, where Olympic Games gold medallist Alexander Zverev beat John Isner 7-6 (7-5) 6-7 (6-8) 10-5 before US Open champion Daniil Medvedev made light work of Denis Shapovalov 6-4 6-0.

Team Europe secured their fourth win of the day in the doubles – Tsitsipas and Andrey Rublev teaming up to defeat Isner and Kyrgios 6-7 (8-10) 6-3 10-4.

After Kyrgios' straight-sets loss to Greece's Tsitsipas, the 26-year-old Australian star casted doubt over his tennis future.

"This is my probably my last Laver Cup," former world number 13 Kyrgios – an Australian Open and Wimbledon quarter-finalist – told reporters post-match. "I don't know how much longer I will be in tennis.

"This is my last event of the year. I will get my body right ahead of the Australian Open.

"My mum is not doing too well with her health. I'd like to go back and see her."

"As long as I'm on the court, I will try and give my best, but I'm not going to lie and say that I'm going to plan to play four or five more years on tour," Kyrgios said. "That's just not me."

Playing for the first time since earning his maiden grand slam trophy at the expense of record-chasing Novak Djokovic at Flushing Meadows, world number two Medvedev suffered no letdown against Shapovalov.

"I played unbelievably, especially [in] the second set," Russia's Medvedev said in his on-court interview. "I didn't know what to expect because after the US Open, I didn't play for a week and a half. Came here, practised as much as I could the past three days, so I didn't hit [that] many balls, but was surprisingly feeling well.

"I wanted to show that also today. [The] first [set] was not easy, the ball was not going as fast as I wanted [and] he was playing really good. And then I just couldn't miss a ball anymore. I'm really happy about [that]."

Team Europe are on track for their fourth consecutive Laver Cup triumph after earning an early 3-1 lead against Team World.

Opening-day honours went to Bjorn Borg's Team Europe at TD Garden in Boston, where the defending champions moved into the box seat thanks to wins for Andrey Rublev, Matteo Berrettini and Casper Ruud in the singles on Friday.

John Isner and Denis Shapovalov managed to get Team World on the board in the evening's final doubles match against Alexander Zverev and Berrettini 4-6 7-6 (7-2) 10-1.

Roger Federer and Rod Laver were in the crowd as Team Europe – headlined by newly crowned US Open champion Daniil Medvedev and consisting of six of the world's top 10 – made a strong start courtesy of Norwegian Ruud, who overcame Reilly Opelka 6-3 7-6 (7-4), improving his career record to 3-0 against the towering American, and beating him in straight sets for the first time.

Italian star Berrettini then overcame Team World's Felix Auger-Aliassime 6-7 (3-7) 7-5 10-8 in the competition's longest match at two hours, 52 minutes.

Berrettini escaped with the second set after facing two break points in the penultimate game before prevailing against the Canadian in a thrilling match tie-break.

"One of the best matches bar none that I've ever seen played, absolutely just enthralling," said captain John McEnroe, whose Team World are eyeing their first Laver Cup trophy.

Rublev rallied past Argentina's Diego Schwartzman, who won the opening set and led 6-2 and 8-5 in the match tie-break before losing 4-6 6-3 11-9.

"Today we are a bit more lucky; Matteo won a tough match against Felix in a super tiebreak, now you saw my match," said Russian star Rublev.

"It was so close; Diego was leading all the super tiebreak, but in the end I find a way to win.

"This happens. This is tennis, this is sport. It’s emotions. Someone has to win, someone has to lose."

On day two, Stefanos Tsitsipas and Zverev headline the day session against Team World's Nick Kyrgios and Isner.

In the evening, Medvedev will meet Shapovalov before Rublev and Tsitsipas team up for a doubles battle with Kyrgios and Isner.

Stefanos Tsitsipas plans to get the COVID-19 vaccine, having previously declared he would only do so if the ATP Tour made it mandatory.

Greek world number three Tsitsipas revealed last month he would not get a jab due to concerns over side effects.

The ATP Tour has persisted in encouraging players to get vaccinated, with Novak Djokovic the most high profile to have stated he was opposed to it, and Tsitsipas has now backtracked on his original stance.

"I will get vaccinated this year," the 23-year-old told Greek outlet Antenna TV. "So I can go to restaurants and shops. I support all those who get vaccinated.

"I am not a doctor; I am a tennis player, so I may not have the most substantiated opinion when it comes to medical issues."

The French Open runner-up was subject to backlash in his homeland following his initial comments on the vaccine, with a series of top figures questioning his thought process.

"The COVID-19 vaccine has not been tested enough because it is new and has some side effects," said Tsitsipas.

"I know some people who've had them. I'm not against it, I just see no reason for someone in my age group to be vaccinated [yet].

"For us young people I think it's good to pass the virus because we'll build immunity.

"I don't see it as something bad. As I said, it isn't obligatory, everyone has freedom to decide for themselves what's right and what's not. At some point we should all do it, I'm not saying the opposite.

"The time will come when we will not be given many options, but until then I want to see a better version of the vaccine that gives us more pluses than minuses."

Tsitsipas is set to play for Team Europe at the Laver Cup this week after missing Greece's Davis Cup tie with Lithuania due to a foot injury.

Nick Kyrgios, John Isner and Reilly Opelka have been named by Team World captain John McEnroe as his final three picks for the Laver Cup.

The trio join Denis Shapovalov, Felix Auger-Aliassime and Diego Schwartzman for the team event which runs from September 24-26 at TD Garden in Boston.

Laver Cup newcomer Opelka rose to a career-high world number 23 ranking en route to his first ATP Masters 1000 final in Toronto and defeated world number three Stefanos Tsitsipas, who will play for Bjorn Borg's Team Europe.

Isner, who has featured for Team World since the inaugural event in 2017, reached the semi-finals in Toronto and claimed his 16th ATP Tour title in Atlanta at the start of August.

He described the Laver Cup as "a highlight of my year", adding: "To be on a team with guys we're normally competing against is so different and so much fun. We come together so well as a group, the chemistry is awesome and it's such a great environment to be part of."

Australian firebrand Kyrgios is a striking inclusion in Team World's roster, while Team Europe will be without their big three: Roger Federer, Rafael Nadal and Novak Djokovic.

Federer and Dominic Thiem were expected to take part in this year's event, though both were forced to withdraw with injuries.

However, Borg's men still boast six of the world's top 11. World number two Daniil Medvedev leads the line-up, with Tsitsipas and Tokyo Olympics gold medallist Alexander Zverev for company.

Casper Ruud, who collected a 14th win in his last 15 completed matches on tour when he beat Opelka on Wednesday, will feature, while Andrey Rublev and Wimbledon finalist Matteo Berrettini complete the six-man team.

Team Europe have landed the title in each of the three editions of the tournament so far, with Prague, Chicago and Geneva having served as hosts.