"Serena is Serena," Sakkari said after advancing earlier on Saturday by beating 19-year-old American Amanda Anisimova 6-3, 6-1. "You have to come up with some great tennis. Otherwise there is no chance against her." Enditem
"My body condition is not a hundred percent, but I'm training every day. I'm giving my best, so that I can help my team as fast as possible," said the former top scorer in Germany's third-tier league.
In Thursday's only other match, Sport Recife won 2-1 at Gremio thanks to goals either side of half-time from Patric Cabral and Iago Maidana. Pepe pegged a late goal back for the hosts. Enditem
There were also third round wins for Belgian star Elise Mertens, Belarussian veteran Victoria Azarenka and France's Alize Cornet.
The reigning champions visited Sweden with their captain Ronaldo back in the squad after the 35-year-old Juventus forward missed their opening Nations League match due to a toe problem three days earlier.
Both sides had chances to break the deadlock in the first half but missed them all. Shanghai Shenhua midfielder Cao Yunding's left-footed shot hit the post in the seventh minute. Shenzhen almost scored the opener in the last minutes going into the halftime break when Ole Selnaes' free kick was also denied by the crossbar.
Mercedes almost immediately elected to pit Hamilton for his scheduled tyre change, but crucially failed to notice that race director Michael Masi had temporarily closed the pit entrance to allow marshals to clear the stricken Haas, earning their driver a 10-second stop-go penalty that put him out of serious contention.
"It was a tough match and we fought hard. It wasn't easy, it could be better in the future," Mbappe said. "The most important thing is the result."
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.
"We are already working hard to achieve our goal of going to Qatar. It's a challenge that affects all of Ecuador. We know it's not going to be easy and we're focused on giving everything we've got."
Developing his squad to a high-speed train might come near a tightrope walk as the German coach knows the challenge.