Roddick's opponent quits match

Andy Roddick advanced to the semi-finals when his Russian opponent Nikolay Davydenko retired in the third set today suffering with breathing problems.

The American was leading 6-3 7-5 4-1 when Davydenko, who began showing signs of distress early in the second set, decided to quit.

Roddick had been forced to save a set point in the second set but was well on top when the Russian called it a day.

The American will now play the winner of today's match between third-seeded Australian Lleyton Hewitt and ninth seed David Nalbandian of Argentina.

Roddick breezed through the first set of his quarter-final clash at the Rod Laver Arena, with one of his eight aces recorded at 142mph.

Roddick had won all three of his previous matches against Davydenko without dropping a set - and he came into the match having spent just over six hours on court so far in the championships.

The 23-year-old used an inhaler and ice vest to combat the high temperature, and even broke Roddick's serve with some power play. But Davydenko - who had beaten Tim Henman in the third round - decided enough was enough when Roddick broke his serve for a second time to lead 4-1 in the third set.

"It's unfortunate it had to end that way," said Roddick, who has lost just one set, against Greg Rusedski, on his march to the semi-finals. "But I'm happy to be through to the semi-finals."