Kerber focused on semi as No. 1 ranking beckons

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 was her opponent.

Angelique Kerber produced a 7-5, 6-0 victory over 2015 finalist Roberta Vinci to reach the last four on Tuesday

Angelique Kerber insists she is taking the US Open on a match-by-match basis as she closes in on Serena Williams' No. 1 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 was her opponent.

The German second seed produced a 7-5, 6-0 victory over 2015 finalist Roberta Vinci to reach the last four on Tuesday, but is not allowing herself to think beyond her next match, which will be against Caroline Wozniacki or Anastasija Sevastova.

"I'm still trying to stay focused on match to match," she said. "When I came here I was telling myself to just play round by round and play my best."

Kerber navigated a patchy first set, in which she came from a break down on three occasions, to claim what became a comfortable victory over Vinci.

"I think it is always difficult to play against Roberta. She is a great player and played so well last year here. She came out to play good tennis. I'm so happy to win it in two sets. To reach the semis here again means a lot to me. I think the key of the match was the first set. It was really close and tough. She's a tough opponent with her slice. I was trying to stay in the match and not think that I'm a break down."

"After I won the first set I was more relaxed at the end. I think in the second set what I did good was that I played the first few games really tough so that I was up 3-0 very fast. Then I could continue my good play in the next few games."