(CNN) -- Roger Federer may have given up his No. 1 ranking, but the Swiss tennis star's grip on end-of-season supremacy is showing no signs of loosening. 

Federer marched into the semifinals of the $5.5 million ATP World Tour Finals on Thursday, beating in-form Spaniard David Ferrer 6-4 7-6 (7-5) for his second successive straight-sets win in Group B. 

The 31-year-old has not lost at the eight-man London showpiece since 2009, and has now won 70 matches this year -- a feat he had not achieved since 2006 when he was at the peak of his powers. 

"This is a very special tournament in many ways," said Federer, who has reached the last four in 10 of his 11 appearances. 

"It's always been the tournament I wanted to be part of when I started playing at the beginning of the year, many years now. I had breakthrough results at this event. I learned a lot. 

"I've loved everywhere I've played over the years at the World Tour Finals. But I think this one is obviously special, because it's in London and The O2 is an amazing venue. I'm happy it's going to stay here for the next few years." 

The 17-time grand slam champion relinquished the year-end top spot to Novak Djokovic when he decided not to defend his Paris title last week, having pushed his record tally to 302 weeks at the top. 

Fifth-ranked Ferrer took advantage of a weakened field and shock defeats for Djokovic and No. 3 Andy Murray by winning his first Masters level tournament, following up his title in Valencia. 
Does he typically perform well at the London showpiece?
I had breakthrough results at this event. 