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 the world number one 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 world number one.
If Kerber reaches the final, then Williams must win the title top 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, because that was also one of my dreams when I was a kid."
Kerber will face Italy's Roberta Vinci for a spot in the semi-finals.