Murray takes the easy route while organisers grant timely extension

Andy Murray hits a return during yesterday's victory over Donald Young (PA)

Andy Murray was expecting to have to win four matches in four days to win the US Open but the 24-year-old Scot received good news here last night after his emphatic fourth-round victory over Donald Young. Under pressure from the players, who had flexed their muscles on Wednesday, organisers agreed to extend the tournament by a day for the fourth year in succession.

Under the revised schedule, the quarter-finals between Murray and John Isner and between Rafael Nadal and Andy Roddick – the winners will face each other in the semi-finals – will be played this afternoon. Novak Djokovic won his quarter-final last night after his fellow Serb, Janko Tipsarevic, became the 19th singles player to quit during the tournament, retiring with a thigh injury when trailing 7-6, 6-7, 6-0, 3-0. Roger Federer and Jo-Wilfried Tsonga were due to play their quarter-final in yesterday's evening session.

Both semi-finals will be played tomorrow, which will give the finalists a day of rest before Monday's final, which will start at 9pm BST. The women's semi-finals (Serena Williams against Caroline Wozniacki and Sam Stosur against Angelique Kerber) will be played tomorrow night, with the final moved to 9pm BST on Sunday.

Jim Curley, the tournament director, said the changes had been the result of "a collaborative effort" between players, broadcasters and tournament officials as a result of the bad weather earlier in the week. Murray, who called yesterday for the players to form their own union, had been at the centre of discussions after Wednesday's controversy, when matches began despite the fact that players had complained that the courts were wet and unsafe. Following the previous day's complete wash-out, only a quarter of an hour's play was possible.

When Murray went on court at 11am yesterday, in sunshine and rapidly rising temperatures, the tournament was still heading for a Sunday finish. The prospect of having to win four matches in four days certainly seemed to concentrate the Scot's mind and he responded with a thoroughly professional display, beating Young 6-2, 6-3, 6-3.

The 22-year-old American, who was playing in the fourth round of a Grand Slam tournament for the first time, carelessly sprayed his forehand to all corners of the court, while Murray was focused on his task from the start. For the most part the Scot played conservatively, but when he needed to open his shoulders he did so. The only area of his game which looked in need of improvement was his serve. He was broken three times and after the match was back on the practice court working on his serve.

If the spectators were slow to turn up on Grandstand Court, Murray was not. While the Scot endeavoured to cut out his mistakes and make his opponent play every ball, Young appeared determined to do the opposite. The world No 84, who had beaten Murray in their only previous meeting in March, made 53 unforced errors to the world No 4's 17.

Beginning the day at 2-1 down, Murray won 10 of the first 11 points and dropped only five more in taking the first set after just 21 minutes. His only major lapse came in the middle of the second set, when he was broken in two successive service games. Early breaks were exchanged in the third, but Murray broke for the eighth time before serving out for victory with an ace.

Isner, who beat Gilles Simon 7-6, 3-6, 7-6, 7-6 to reach his first Grand Slam quarter-final, lost to Murray in their only meeting in last year's Australian Open. "He's got a huge serve and can hit big forehands and is a little bit erratic and doesn't give you much rhythm," Murray said of the 6ft 9in American.

Murray said the controversy of the previous day would not have happened at a tournament on the Association of Tennis Professionals tour rather than at a Grand Slam event, which is run in conjunction with the International Tennis Federation. "Because we have the ATP and the ITF, and they don't like each other very much, there's always going to be some issues," Murray said.

The ATP is run jointly by players and tournaments. Murray said it was time for the players to form their own body. "I think players need to have more of a voice and the only way to do that is by starting a player union," he said. "If not, the same things will keep happening and nothing will change."

Murray said he was unhappy with the scheduling of matches here –particularly playing the first round over three days and the semi-finals and final on successive days – and with the fact that there was no attempt to cover the courts during rain delays.

He hopes the players will discuss the big issues at next month's Shanghai Masters. "There are a lot of things that need to be changed aside from just maybe some of the scheduling here," he said. "I think the sooner it's done the better for everyone."