The US women came to Tokyo as firm favourites but Biles admitted to feeling the pressure
The O2 Arena is hosting the ATP Finals for the 12th and final season before the year-end championships moves to Turin next year.
Liverpool keeps up with Everton at the top of the Premier League table.
Jurgen Klopp is on the brink of leading Liverpool to a first league title in 30 years.
Arteta's team are nine points adrift of the top four.
It is Tsitsipas's third title of the season and comes a year after he was crowned champion at the Next Gen ATP Finals in Milan.