Murray will play Mardy Fish in the quarter-finals on Friday

Henman took a straight-sets victory over Jan-Michael Gambill while Murray saw off Feliciano Lopez 7-5 6-2.

Murray will now play Mardy Fish, while Henman takes on his old Russian foe Dmitry Tursunov.

Murray said: "It'll be a difficult match. Mardy finished five hours before me. He'll get more time to rest."

Henman took just one hour and 13 minutes to wrap up a comprehensive 6-1 6-3 victory.

It went from pretty light to pitch black Andy Murray on the Washington weather

The tone was set in the opening game with Henman breaking the American's serve.

He maintained the momentum at the start of the second, breaking for a 2-0 lead as Gambill's serve continued to let him down.

Murray, meanwhile, led 5-4 in the first set when showers halted play for over two hours.

Murray said: "It went from pretty light to pitch black.

"It was a different match when we got back - the ball was a lot slower.

"But as long as you are sharper than your opponent, you will make the better start."

Marat Safin had one of his best results since coming back from a knee injury as he beat top seed and world number five James Blake 7-6 (8-6) 7-6 (7-5).

"These kind of matches are the most important," said the Russian.

"Playing good, bad, with a lot of luck - these are the ones that are going to give you the confidence."

Third seed Lleyton Hewitt eased into the quarter-finals with a comfortable 6-1 6-4 win over Denis Gremelmayr.