Third seed Williams essayed a signature comeback and served 12 aces to edge past her American compatriot Stephens 2-6, 6-2, 6-2 in one hour and 43 minutes.
"In accordance with the Grand Slam rulebook, following his actions of intentionally hitting a ball dangerously or recklessly within the court or hitting a ball with negligent disregard of the consequences, the US Open tournament referee defaulted Novak Djokovic from the 2020 US Open," organizers said in a statement.
"I'm very happy to play a tough game with such wonderful shuttler. I was not cautious enough today and I felt nervous on some key points. But generally I think I performed well," said Chen.
Williams's ambition of securing a record-equaling 24th Grand Slam title remains alive as she moved into the women's quarterfinals after an immensely hard-fought 6-3, 6-7 (6), 6-3 victory over Maria Sakkari of Greece, while Thiem had a much easier time with a 7-6 (4), 6-1, 6-1 win against Canadian rising star Felix Auger-Aliassime in the men's draw.
"You can feel it in your body when you have a good throw, mostly you feel the whole energy behind it, from the right toe to the chest to the hands. In the javelin you need your whole body. But it's really hard to explain - you feel it for less than one second. But then you realize that it was a huge throw," he explained.
The start of the race was done in smaller groups of a few hundred people, as opposed to the usual big launch of several thousand.
Other high-profile South Americans playing in the Chinese Super League include Brazilians Oscar (Shanghai SIPG), Hulk (Shanghai SIPG), Renato Augusto (Beijing Guoan) and Paulinho (Guangzhou Evergrande), as well as Venezuela international striker Salomon Rondon (Dalian Pro). Enditem
Belgium swept Iceland 5-1 at home to lead Group 2 with two wins, and Denmark drew 0-0 with England as both teams failed to create good chances. Enditem
The Kenyan now will return to her 1,500m specialty against Dibaba with hope of continuing her perfect start to Diamond League series at the Ostrava Golden Spike (Czech Republic) on Tuesday.
Djokovic immediately rushed over to check if she was okay and placed his hand on her back as she struggled for air. After a few minutes she was able to get up and walk off the court.
"I was playing well today," said Thiem. "I had a good plan for the match. He's very dangerous when he can dictate with his forehand. I was exactly trying to avoid that. He also has very, very fast legs. I was trying to play my fastest tennis to keep him on the backhand, to not let him dictate with the forehand."