It was also a disastrous race for Red Bull, with Max Verstappen retiring from the midfield with engine trouble, and Alex Albon finishing down in 15th after a scrappy performance in which he received a five-second penalty for impeding Romain Grosjean's Haas.
Stephens went up a double break to carve out a 5-2 lead and served out the opening set in just 38 minutes. But Williams began to raise her game and served much better in the second set, lifting her first-serve percentage from 50 to 76 percent. By breaking twice, Williams won the second set to level the match.
"This is my duty to know my team's weaknesses since I don't want to waste my time," the Croat added.
Finishers got their running medal in their hand, not on their neck.
"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 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. I did that very well today."
Last season saw goalkeeper Thibaut Courtois show why Madrid signed him from Chelsea, while the defense of Sergio Ramos, Raphael Varane, Dani Carvajal and Ferland Mendy was the tightest in the league.
Messi failed to appear for routine PCR tests on August 20 ahead of Barca's return to training, and did not attend any of the sessions under new coach Ronald Koeman.
Then in the third set, Williams was rarely troubled by her rival en route to victory.
In a rematch of their 2020 Australian Open quarterfinal, the second seed recovered from a 4-2 deficit in the opening set to overcome Jabeur. It's the first time Kenin has reached the fourth round at the US Open.
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.
"I just don't know what to say, it was really close to a perfect moment," Vetter told World Athletics.