Andy Murray will head to New York this weekend knowing there is plenty of work still to be done if he is to retain his US Open title after he was beaten by Tomas Berdych in the quarter-finals of the Cincinnati Masters last night.

The Scot was some way off his Wimbledon-winning best against an on-song Berdych and the world No.2 was well beaten by the Czech, going down 6-3, 6-4. As he heads to Flushing Meadows, Murray will not allow himself to become unduly worried about his form, though, despite relatively early defeats in back-to-back Masters 1000 events.

However, last night's defeat could yet make his US Open defence that much trickier, especially as Rafael Nadal - who was due to play Roger Federer in the remaining quarter-final - could overtake him as No.2 should he win the title this week. That would leave Murray seeded No.3 in New York and facing the unappetising prospect of having to defeat both Nadal and world No.1 Novak Djokovic to win the third grand slam title of his career.

Berdych clearly enjoys playing Murray, having now won six of their 10 encounters, and last night the Czech had an answer to everything Murray was able to muster. The Scot had begun the match with four straight aces in his opening service game but once he had missed an early break point opportunity, he never looked fully at ease.

The music blaring out from the adjacent Centre Court was a distraction for both players and though Murray produced some fine play at times, he was guilty of mistakes when he was in a strong position.

Armed with physical power on a day when there was no wind to affect his high ball-toss, Berdych was comfortable and played with confidence throughout. Having saved two break points at 1-2, Murray found himself in trouble again at 3-4 and an errant forehand - his weak side throughout the match - gave Berdych the break before he served out easily for the first set.

Murray opened the second set with a good hold and looked likely to break when he forced 0-40 on the Berdych serve. But again, the Czech player came up with some brave shots when he needed it to hold his nerve and then, having got out of jail, he took his third break point to move ahead 2-1 and take charge.

Murray continued to hang in there on serve to at least force Berdych to serve out the match but the Czech, whose nerve has been questionable in the past, did so with ease to claim a morale-boosting victory.

While Murray will now head to New York to hone his game under the watchful eye of Ivan Lendl, Berdych will play Juan Martin Del Potro in today's semi-finals after the latter defeated Russian qualifier Dmitry Tursunov 6-4, 3-6, 6-1.

If Murray was looking for any consolation before he left, he might have found it in a shock defeat of Djokovic as he was beaten 7-6, 3-6, 7-5 by American John Isner.

Isner, who will move back into the world's top 20 as a result, missed nine break-point chances before finally taking his 10th, on his second match point, to record his best victory of the year.

Djokovic looked strangely out of sorts throughout and was blunt about his own performance, the last two points of which were a double-fault and an ugly backhand into the net. "I played a very bad match overall," he said. "It was a terrible match."

In the women's event, world No.1 Serena Williams maintained her hard-court winning streak as she defeated Simona Halep of Romania 6-0, 6-4 to set up a semi-final with Li Na of China.