NEW YORK • Angelique Kerber reached the US Open quarter-finals on Sunday, which left Serena Williams needing to reach the final to have a chance of retaining her world No. 1 spot.
Kerber defeated Petra Kvitova 6-3, 7-5 to pile the pressure back on to the American, who is looking to break Steffi Graf's record of 186 weeks as the top-ranked player in the world.
If Kerber reaches the final, then Williams must win the title to stay on top of the pile.
"When I was a kid, of course I was dreaming of winning Slams and being one day No. 1, and now it can happen," said Kerber.
"But I'm trying to not put pressure on myself, because I know I have to win a few more matches to reach the No. 1.
"When it happens it will be an amazing feeling."
Kerber, who will face Italy's Roberta Vinci for a spot in the semi-finals, was in command from the start against Kvitova, winning all the big points on the way to taking the opening set.
Kvitova, the Rio Olympics bronze medallist, offered more resistance in the second set before surrendering with a double-fault on match point.
Playing textbook counter-punch tennis, Kerber had eight winners and just eight unforced errors.
Kvitova, by contrast, was far more aggressive, but her 32 winners could not make up for the 43 unforced errors - 27 coming off her forehand alone.
"I felt I played a little terrible," said Kvitova.
"It wasn't really nice tennis. I was trying. I felt like I really made the chances but I just didn't take them."
Vinci, last year's runner-up, reached the quarter-finals for the fourth time but had to shrug off a tendon injury in her leg to prevail.
"I love to play here. The atmosphere, the crowd, everything is great," said the Italian, who knocked out Williams in the semi-finals last year before losing the final to compatriot Flavia Pennetta.
Kerber and Vinci are 2-2 in head-to-head meetings but have not played since Beijing in 2013.
AGENCE FRANCE-PRESSE, REUTERS