Angelique Kerber admitted she struggled for focus in her US Open semi-final against Caroline Wozniacki after witnessing the Serena Williams defeat that made her the new world number one.

Top seed Williams was beaten 6-2 7-6 (7-5) in her last-four clash with Karolina Pliskova, consequently losing her place at the top of the rankings, where she had sat for a record-equalling 186 weeks, to the German.

Kerber - the Australian Open champion who also finished as runner-up at Wimbledon - confessed that stepping onto the court knowing she was world number one made it difficult to concentrate.

However, the 28-year-old came out on top against Wozniacki 6-4 6-3 to set up a meeting with Pliskova in Saturday's final and was pleased to have won an internal mental battle.

"I watched the last few points. I knew it would be tough because I know Pliskova has been playing very good in the last few weeks. I played against her in Cincinnati," said Kerber.

"It was not so easy to go on court then, because I knew it actually before that if Serena lost, of course, that I will be the number one. So it was not so easy mentally, but I was trying to, again, not put too much pressure on myself.

"That shows me that I think I'm growing and I'm not putting the pressure on my shoulders if something like this happens. I can go out there focusing on my game. That gives me also a lot of confidence with the situation, how I dealt with it today."

Having become the first German to top the rankings since Steffi Graf, Kerber claimed she had achieved one of her dreams.

"It feels amazing. Yeah, it feels just great. The day came today, and to be now the number one in the world, that was always a dream for me," she added.

"I was trying to not think too much the last few weeks about this, and now I've reached it, so it's something really special for me."