ARGENTINA'S Juan Martin Del Potro ended top seed David Ferrer's reign as Japan Open champion with a 6-1, 7-5 quarter-final victory.

Fifth seed Del Potro, whose heroics helped Argentina reach the Davis Cup final last month, never looked like losing his grip on the match after a rousing start against the Spanish world No.5.

"With Ferrer you never feel you have the edge," said the 20-year-old, one of several players at the Tokyo event chasing a spot in the season-ending Tennis Masters Cup.

"I've improved my mental preparation. I'm more positive now than before. That helped me put Ferrer away when he came back at me in the second set."

Del Potro faces fourth seed Richard Gasquet in tomorrow's semi-finals after the Frenchman crushed German 12th seed Rainer Schuettler 6-3, 6-2.

Del Potro tore through the first set in just 27 minutes against a listless Ferrer, who lifted his game in the second but ran into a red-hot opponent.

The lanky Argentine broke for 5-3 only for Ferrer to immediately claw back the break but was unable to repel Del Potro's onslaught for long.

Ferrer, who suffered an embarrassing early exit in Beijing last week, had little left in the tank against a player he is set to meet again in next month's Davis Cup final in Argentina.

Sensing Ferrer's energy levels were low, Del Potro moved in for the kill as the Spaniard served at 5-6, finishing off the match with a crushing forehand into the corner.

A fifth title of the year would move Del Potro into the coveted eighth spot in the year-long rankings and in line for a place at the next month's prestigious Masters Cup.

Rafael Nadal, Roger Federer, Novak Djokovic and Andy Murray have already qualified for the eight-man Shanghai shootout.

n Andy Murray has qualified for Masters Cup