The year-end championships have been Federer's domain, with the 31-year-old winning six titles, including the last two years, and only failing to make the semi-finals in Shanghai in 2008.

It was not vintage Federer but he found an extra gear when he needed to, saving nine out of 10 break points he faced to make it 29 sets won out of 32 against Ferrer.

The world number five has had a brilliant year and went into the clash on an 11-match winning streak after titles in Valencia and Paris, and he was left to rue his missed chances.

While an advantage in head-to-head record is obviously a confidence boost, Federer admitted to feeling the pressure of trying to maintain such a long streak.

The 31-year-old also recalled the first tournament at the O2 in 2009, when Nikolay Davydenko ended a 12-match losing run against him in the semi-finals and went on to win the title.

Federer said: "Streaks have ended for me at the World Tour Finals. There was Davydenko and (Fernando) Gonzalez as well years ago when he beat me for the first time.

"In some ways it's helpful to have that one-sided head-to-head record, but at the same time it sometimes creates pressure as well. You always feel like this next match it is probably going to happen.

"You try hard, he tries harder too because all he needs is that one win, so then he's got that.

"I tried hard to not make it happen today. You could feel that he's confident, he's on a run. I think it's a great victory for me."

Ferrer felt he missed his opportunity to pile pressure on Federer at the start of the match when the Swiss star was not serving well but still moved into a 3-0 lead before his opponent eventually broke back at the eighth time of asking.

Ferrer said: "I had a lot of chances to break him but I couldn't do it. When he has one break point on my serve, he makes it.

"Sometimes with these players, if I don't take my chance, I don't win the important points, it is very difficult to win these matches."

Ferrer will still have a good chance to reach the semi-finals if he beats Janko Tipsarevic in his final round-robin match on Saturday, and if he then makes the final he will overtake injured compatriot Rafael Nadal to become world number four.

Ferrer played down the significance, though, saying: "I don't think about that because Rafa is injured. I don't care if I finish four or five in the world.

"I am trying to do my best to have a great tournament here. Then next week I will have a very important Davis Cup final."

In the evening match Del Potro needed only an hour and 16 minutes to defeat a below-par Tipsarevic 6-0 6-4, and the Argentinian will reach the semi-finals if he beats Federer tomorrow.

Del Potro gave the packed crowd some extra entertainment after the match when he knocked up with compatriot and Manchester City striker Sergio Aguero, who had been supporting his friend.

The 24-year-old said: "He's a good soccer player. He is a really, really nice friend, a really nice guy. I think he enjoyed my match today, and also he can hit the ball really well."

Del Potro had hit with another Manchester City striker, Carlos Tevez, on the same court in 2009 while waiting to discover whether he had reached the semi-finals.

Tipsarevic has been struggling with illness for the past week but vowed to play his last match against Ferrer even though he now has no hope of qualifying.

The Serb said: "I'm playing horrible. I'm playing worse than horrible. I'm playing the worst tennis that I played in a long time. But I'm on the court, behaving good, not throwing my racquet, giving my best.

"I am generally feeling fine. The problem was that I was sick and I didn't play a lot of tennis lately.

"I feel sorry that I don't play my best tennis here in London, which is probably the best event of the year. But I fought hard to be in a position to come to this event. So I'll just do my best for one more match."