Angelique Kerber insists she is taking the U.S. Open on a match-by-match basis as she closes in on Serena Williams' No. 1 world ranking.
Williams must reach the final at Flushing Meadows to have a chance of retaining top spot and would need to win that match if Kerber were her opponent.
The German No. 2 seed produced a 7-5, 6-0 victory over 2015 Open finalist Roberta Vinci to reach the last four on Tuesday, but is not allowing herself to think beyond her next match, which will come against a rejuvenated Caroline Wozniacki.
"I'm still trying to stay focused on match to match," Kerber said.