The Japanese player has been fined £12,900 (€15,000) after deciding to boycott press conferences at the tournament. Osaka announced on Wednesday that she would not be conducting press conferences at the tournament, which began on Sunday and runs until May 13.
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Nadal trailed 4-2 in the opener but recovered, breaking twice to take it.
Federer, 39, is making his comeback after two knee operations and has not played a Grand Slam since January 2020.
Djokovic produced a clinical 6-4 6-2 win over up-and-coming Jannik Sinner on Wednesday before Nadal, the 11-time champion at the Country Club, thrashed Federico Delbonis 6-1 6-2.
Federer, who has needed two operations to correct a long-standing knee issue, is due to play in the Qatar Open this week.
His latest triumph in Melbourne has brought the 33-year-old world number one Djokovic to within two of the record mark of 20 major wins shared by Roger Federer and Rafael Nadal.
The 23-year-old defeated first-time slam finalist Jennifer Brady of America 6-4 6-3 to regain the title she won in 2019.
The world number one, who has won the title on each of the eight previous occasions he has reached the semi-finals in Melbourne, claimed his first straight-sets win since the first round, beating the world number 114 6-3 6-4 6-2.
The mother of one could barely respond before her voice broke and she began crying, leaving the room and ending her press conference.
Williams gave the crowd inside the Rod Laver Arena a long wave goodbye with her hand on her heart following her 6-3 6-4 semi-final defeat by Naomi Osaka.
Second seed Nadal was on course for a comfortable victory before Tsitsipas turned the match around to prevail 3-6, 2-6, 7-6 (7/4), 6-4, 7-5 in a seismic upset.
The second seed came into the tournament with serious concerns over a back problem but revealed after beating Britain’s Cameron Norrie in the third round that it had finally started to improve.
Both advanced into the fourth round of the competition in five-set thrillers.
The 40-year-old American, a seven-times Grand Slam winner and twice finalist at Melbourne Park, suffered a 1-6 0-6 defeat.
Also, world number three seed Naomi Osaka cruised past Russian Anastasia Pavlyuchenkova 6-1 6-2.
Williams, the winner of 23 Grand Slam singles titles, had set up a mouth-watering semi-final clash against world number one Australian Ash Barty after defeating fellow American Danielle Collins 6-2 4-6 (10-6) on Margaret Court Arena.
Victorian state Premier Daniel Andrews said the man last worked at the Grand Hyatt Hotel in Melbourne on January 29 and anyone there was considered a casual contact.
The players did something different by soaking up their freedom after 14 days of quarantine ahead of the Australian Open.
“Gutted to share that I won’t be flying out to Australia to compete at the Australian Open,” Murray was quoted as saying by British media on Friday.
The demand for a reduction was due to players’ inability to train at required level amid the strict COVID-19 quarantine rules.