(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.
However, the 30-year-old had never beaten Federer in 13 previous attempts, winning just three of 30 sets played -- including defeat to Federer in the 2007 final of the elite event when it was held in Shanghai.
That run continued on Thursday after Ferrer failed to covert three break points on Federer's serve in the opening game.
"It was a long match and I'm extremely happy to win," Federer said after ending Ferrer's 11-match unbeaten run.
"I played a great match. I've qualified and I'm obviously relieved and thrilled that that's the case.
"David's been on a great run and he is so respected by his fellow competitors. I enjoy playing against him, not because I've got a good record, but because he's a great guy and a great competitor."
Federer now has a 102-1 record against players aged over 30 since his 2002 defeat by Andre Agassi in the final of the Miami Masters.
If he retains his title, extending his record to seven overall in the indoor hard-court event, he will match third-placed John McEnroe on the ATP's career title list with 77.
Ferrer has won an ATP Tour-leading 73 matches this year, one more than Djokovic -- who will seek to clinch his semi spot in his third and final closing Group A match against sixth-ranked Czech Tomas Berdych on Friday.
Ferrer, who also has a tour-leading seven titles in 2012, must now beat Janko Tipsarevic if he is to emulate last year's achievement of reaching the semifinals in London.
"I had a lot of chances to break his serve," Ferrer said of his latest Federer defeat. "When he had one break point, he made it.
"Sometimes with these players, if I don't take my chances, I don't win the important points -- it is very difficult to win."
Ferrer is fighting for a semifinal place with Juan Martin del Potro, who beat Tipsarevic 6-0 6-4 in Thursday's late match to end the Serbian's hopes.
The Argentine now also has one win and a defeat ahead of his final match against Federer, but has the advantage over Ferrer in sets and games won.
Del Potro beat Federer in last month's Basel final but has a losing 13-3 record against him despite notable victories in the 2009 U.S. Open title match and in the round-robin stage of that year's ATP finals.