A warm-up typically held in Cincinnati is also being held at the US Open venue to ensure a safer transition and Williams narrowly escaped against Arantxa Rus of the Netherlands in their opener.
Williams led 4-1 in the third but was two points behind Rus's serve loss at 6-5. The American stepped up play in the final tie-breaker to rob the left-hander of what would have been a huge moment after heartbreak earlier in her career. Rus lost 17 consecutive games from 2012 to 2013.
It was Williams' longest outing since a loss at Roland Garros in 2012 to Virginie Razzano - the only time the 23-time Grand Slam winner has come out in the first round of a Grand Slam - and only the second time in over 20 years. career, she played back-to-back tiebreakers in the third set.
Like next week, no fans are allowed on site, prompting Williams to look back on the '80s when few people were watching her as a junior.
"At one point I was pumping my fist and saying, 'Come on, come on. I had a crowd in my head or something, "Williams, who turns 39 next month, told reporters. "It was really funny for me. I do not know. For me, it was like there was a crowd there.
"I feel like I'm back in the juniors but on a bigger level in a weird way, because it wasn't that much ... it takes you back to the 80s", a- she said later. "Yeah. Wow, it's been a long time."
Her preparation for what would be a record 24th major continues in Tuesday night's session against one of the game's most promising players, 13th seed Maria Sakkari.
Djokovic's injury
Novak Djokovic also plays on Tuesday after beating qualifier Ricardas Berankis.
He wasn't as close to defeat as Williams but worked for a 7-6 (2) 6-4 win, perhaps no surprise given the layoff from official games, his problem with neck and her positive coronavirus test after her controversial Adria tour the exhibition was halted.
Djokovic had eight aces but also seven double faults, which he attributed to the neck problem that forced him out of the doubles event.
"It bothered me," said the Serbian, who then meets Tennys Sandgren. "I've done so many double faults, and he knew exactly where I'm going to serve. There weren't a lot of options for me because of the sticky situation I was in.
"But I somehow succeeded with the great help of the physiotherapist ATP, who did their best to make me feel better. That's what it is. I mean, j tried to play one game at a time. "
He has improved to 19-0 this campaign.
Djokovic's main rivals Roger Federer and Rafael Nadal are not competing this week or at the US Open. Federer is recovering from knee surgery and Nadal is skipping events due to the pandemic.
But other 'Big Four' member Andy Murray plays and the Scotsman - who underwent hip resurfacing last year to save his career - defeated Alexander Zverev 6-3 3- 6 7-5 for a first top -10 scalp since Roland-Garros 2017.
Double faults
Zverev recovered from a break deficit in the third to lead 5-4 but was unable to serve the game. The German was defeated by even more double fault issues, hitting five in his last two service games and 11 overall.
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Murray then gets another big server at Milos Raonic, a rematch of the 2016 Wimbledon final won by the first. Raonic, however, only managed five double faults and managed 23 aces to beat fellow Briton Dan Evans 6-3 7-5.
The biggest upheaval came from Djokovic's good friend Filip Krajinovic, who beat Dominic Thiem 62 61 in an hour. Thiem, who lost to Djokovic in five sets in the Australian Open final, won just two of 34 return points, which is part of what the Austrian called "horrific statistics. ".
