Roger Federer is unconcerned about playing his Stuttgart Open semi-final with the added pressure of the world number one ranking being on the line.

The 20-time grand slam champion returned to the top of the rankings for the first time in over five years in February, and, after beating Guido Pella 6-4 6-4 on Friday, he is just one match away from regaining the position from Rafael Nadal.

Standing in Federer's way is Nick Kyrgios, who defeated Feliciano Lopez 6-4 3-6 6-3.

"Funny enough, I didn't think of it," Federer said of the number one ranking after his win over Pella.

"I was really just focused on the task at hand. But I'm sure that the next match, especially now that you reminded me as well, I will think of it. It's all good. In the match that you play for world number one, it's clearly going to be in the back of your head."

"I thought I was in good control. I thought I served well. I didn't give Guido many chances to get into my service games, except maybe the last couple. I was happy that I also got more rhythm."

Tomas Berdych was left to rue failing to convert the only two break points that came his way against Milos Raonic, who set up a semi-final against Lucas Pouille – a 6-4 6-7 (5-7) 6-3 victor against Denis Istomin – by triumphing 7-6 (7-2) 7-6 (7-1).

At the Rosmalen Grass Court Championships, Bernard Tomic made his first ATP Tour semi-final in two years with a 6-4 7-6 (7-3) win against Fernando Verdasco.

Second seed Richard Gasquet awaits following his 7-6 (7-2) 7-6 (7-4) victory over Stefanos Tsitsipas, while Jeremy Chardy and Matthew Ebden will contest the other last-four clash.