France's 32nd seed Gael Monfils takes on Mardy Fish hoping to reach the quarter-finals of the US Open for the first time

But the Frenchman has little to celebrate on his 22nd birthday as he is injured soon after losing the first set

And it is Fish who books his place in the last eight with a comprehensive straight-sets victory

Germany's Anna-Lena Groenefeld stands between in-form sixth seed Dinara Safina and a quarter-final place

Safina has to battle to take the first set 7-5 but does not lose another game as she wraps up her victory in double-quick time

World number one Rafael Nadal looks in supreme form as he takes the first set 6-2 against Sam Querrey

But Querrey - ranked 55th - is backed by a partisan home crowd and the American fights back from 5-3 down to take the second set

Nadal steadies the ship by taking the third set on a tie-break but the Spaniard is still struggling with his serve

And Nadal is hugely relieved when he finally seals a 6-2 5-7 7-6 (7-2) 6-3 win and a place in the last eight

Former world number one Amelie Mauresmo enjoyed a return to form in the first week at Flushing Meadows

But Italy's Flavia Pennetta has too much for Mauresmo in round four, winning 6-3 6-0 to reach her first Grand Slam quarter-final

Venus Williams has few problems in seeing off Agnieszka Radwanska of Poland 6-1 6-3

Serena Williams sets up a quarter-final against her sister with a comprehensive win over France's Severine Bremond

Argentina's Juan Martin del Potro continues his incredible run by notching his 23rd consecutive win as he sees off Kei Nishikori

British number one Andy Murray plays on Arthur Ashe Stadium for the first time as he takes on Stanislas Wawrinka in the night match

And Murray makes a blistering start to his match, breaking three times in the first set and midway through the second

Wawrinka, the 10th seed, can do nothing to halt the onslaught from Murray as he drops serve in the third set

Murray wraps up a 6-1 6-3 6-3 victory in one hour 49 minutes, setting up a quarter-final against Del Potro