The muscular world number two overcame a slow start and a left knee problem to break the Russian in the second and third sets, winning 5-7, 6-4, 6-4 in two hours and 43 minutes.

Nadal became the last player to qualify for the last four with James Blake already assured of top spot in the Gold Group.

Blake will meet defending champion David Nalbandian in the semi-finals. The American was due to face the already eliminated Tommy Robredo in a dead rubber later on Friday.

In his first meeting with Davydenko, Nadal struggled with his serve and found his baseline game neutralised by the Russian in a first set that clocked in at 66 minutes. A nervy double fault at 5-6 cost him the set.

The Spaniard hit back immediately, converting his second break point of the next game and levelling the match when Davydenko sent a forehand wide on set point.

Nadal appeared in trouble after the second game of the decider when he called for the personal trainer and had his left leg strapped below the knee.

But he rallied to conjure three break points at 3-3, converting the third when he forced Davydenko wide and the Russian netted with a forehand.

He faced his first break point of the set when serving for the match but thundered two service winners before winning his first match point when Davydenko fired wide.

Nadal is making his Masters Cup debut this year after missing the 2005 tournament with a foot injury.

The Spaniard dominated early in the season, beating Federer in four finals on the way to five titles, including his second consecutive French Open crown.

But his form slumped after he lost the Wimbledon final and he has not made it past the quarterfinals in any of his six regular-season tournaments since.

Davydenko has reached a career-high number three ranking after a globe-trotting year in which he played 31 tournaments before the Masters Cup.

The world's top eight players compete in the 4.45-million-dollar tournament, which is in a round-robin format ahead of the semi-finals and final on Saturday and Sunday.