Roger Federer survived a second-set meltdown to beat Argentina's Guillermo Coria 6-0, 1-6, 6-2 at the season-ending Masters Cup on Thursday, giving the Swiss his 80th win of the year.

World number one Federer, who had already secured his place in the semi-finals, extended his winning streak to 34 matches as he seeks a third straight Masters title.

Only Ilie Nastase in 1971-73 and Ivan Lendl in 1985-87 have won three in a row.

Federer inexplicably fell apart in the second set after pummelling Coria in the first.

Coria had called the trainer to treat his left ankle after slipping 5-0 behind in the first set and the Argentine looked a totally different player in the second.

But normal service was resumed in the third and Federer gained the decisive break to go up 4-2 before closing out the match on a Coria double-fault after one hour, 24 minutes.

Federer improved his win-loss ratio for the year to 80-3 and is now just two wins away from matching John McEnroe's professional-era record of 82-3 for a season in 1984.

Coria lost all three of his Red Group matches on his third appearance at the year-ending championships.

Russia's Nikolay Davydenko and Argentine David Nalbandian have joined Federer in the last four.

Argentina's Gaston Gaudio plays Chile's Fernando Gonzalez on Friday for the remaining semi-final spot.