UPDATE 1-From mute buttons to Hunter Biden: Four takeaways from the Trump-Biden debate

(Adds debate starting)

By Andy Sullivan

Oct 22 (Reuters) - Trailing in opinion polls with the Nov. 3 election fast approaching, President Donald Trump is under pressure to revive his flagging campaign in Thursday's final presidential debate with Democratic rival Joe Biden.

Here are some things to watch for in the debate, which began at 9 p.m. EDT (0100 GMT Friday):

A CIVILIZED START

After the first Trump-Biden debate in September devolved into a chaotic shouting match, moderators said they would mute each candidate's microphone to allow the other to speak without interruption for two minutes at the outset of each 15-minute debate segment.

The mute button is not being used, however, for the remaining 11 minutes of each segment, so there is still plenty of opportunity for the candidates to mix it up.

Whether thanks to the mute button or not, the debate got off to a relatively civil start as the two candidates made their opening statements and allowed each other to answer questions from moderator Kristen Welker without interruption.

Trump, in particular, seemed to be on his best behavior. Viewers largely panned his performance in the first debate, in which he repeatedly interrupted Biden.

THE PANDEMIC

Shortly after the last debate, Trump contracted COVID-19 and spent three days in a hospital. The pandemic, which has killed more than 222,000 people in the United States, remains the top issue for voters and Biden has repeatedly accused Trump of mismanaging the crisis.

"I caught it, I learned a lot. Great doctors, great hospitals," Trump said.

Organizers had planned to install a plexiglass barrier between the two candidates to reduce the risk of infection, but they took it down after Trump tested negative for the virus.

Members of the Trump family did not wear masks at the last debate. For this one, they arrived with masks on.

THE COURTS

While it is not listed as one of the debate's official topics, the Supreme Court could become a flash point.

Trump's third nominee, Amy Coney Barrett, is on track to win Senate confirmation to the high court next week, likely locking in a 6-3 conservative majority for years to come.

Biden has been under pressure to explain whether he supports a proposal by some Democrats to expand the nine seats on the court to dilute the influence of those conservatives.

Biden said earlier on Thursday he would support a bipartisan commission to consider the issue.

BIDEN'S SON

Trump has sought since last year to portray Biden as corruptly involved with his son Hunter's business dealings in Ukraine and China, although an investigation by the Republican-led Senate Intelligence Committee turned up no evidence to support that allegation.

In fact, the only result has been Trump's impeachment last year by the House of Representatives for pressuring Ukrainian President Volodymyr Zelenskiy to investigate Biden.

Trump is still at it. Before the debate, Trump's campaign introduced a former business associate of Hunter Biden named Tony Bobulinski, who has agreed to cooperate in a Senate investigation of the Bidens.

Look for Trump to bring that up during the debate in an attempt to rattle Biden. He did not have much success last time: When he mentioned Hunter's illegal drug use, Biden said he was proud of his son's efforts to overcome addiction.

Trump and his children have been accused of conflicts of interest of their own since he entered the White House, most involving the family's real estate and hotel businesses in the United States and abroad.

(Reporting by Andy Sullivan; Editing by Scott Malone and Peter Cooney)