Shoulder injury puts Laura Robson out against Sloane Stephens as Andy Murray powers through against Ricardas Bernankis

After the ecstasy, the agony. Forty-eight hours after her stunning victory over Petra Kvitova, Laura Robson made a painful exit from the Australian Open here today after a shoulder injury scuppered her chances of winning an eagerly awaited confrontation between the two most exciting teenagers in the women's game.

Sloane Stephens, who at 19 is just 10 months older than Robson, won 7-5 6-3 to secure her place in the fourth round. Robson's departure left Andy Murray in the familiar position as Britain's final representative in singles competition, the Scot having moved smoothly into the last 16 with a 6-3 6-4 7-5 victory over Lithuania's Ricardas Berankis.

The injury was a desperate stroke of bad luck for Robson, who had first felt a problem after a practice session on yesterday evening. She had her left shoulder taped before she went on court, but in the middle of the first set she sent for a trainer and doctor and took a medical time-out. She needed further treatment during subsequent changeovers.

The extent of the problem was evident in the average speed of Robson's first serve, which was 105mph in her victory over Kvitova but dropped to 94mph today. The world No 53's big leftie serve is usually one of her biggest weapons, but on this occasion she did not hit a single ace. Her booming ground strokes also lost some of their potency, which was reflected in her tally of just 11 winners, half the number struck by Stephens, whose one significant weakness is normally her lack of power.

“Physically I was fine up until last night,” a subdued Robson said after the match. “I felt something in my shoulder yesterday. We still don't know what it is because I haven't had time to see the doctor, but these things happen. You just have to play through the pain sometimes.”

In the circumstances Robson did well to push Stephens as hard as she did. The world No 25, who has been taken under the wing of Serena Williams and is regarded as her country's greatest prospect, is a superb athlete with a fine all-round game. Her defensive qualities in particular are outstanding. Robson, her painful shoulder notwithstanding, regularly had Stephens at full stretch but the American kept making her hit the extra shot.

The match was surprisingly staged on Court Two rather than one of the three main show courts. Robson, who was born in Melbourne, is hugely popular in these parts and the court was packed with her noisy supporters, many of whom had taken their seats during the previous match to guarantee their place. “I felt like I was playing an Italian player in Italy,” Stephens said afterwards. “It was crazy.”

Robson said: “It was amazing. I was really quite shocked to see the whole court was full. There were so many British people, maybe some Australians supporting me as well, which is good. They were very loud.”

Stephens took a 4-0 lead inside a quarter of an hour, but Robson promptly levelled at 4-4. However, when the Briton served at 5-6 and 30-30 Stephens played two points which summed up the match. A 24-stroke rally, in which Robson had been typically aggressive, ended with the world No 53 netting a forehand. On the next point she hit a backhand long after another lengthy baseline battle.

Stephens, who won their only previous meeting at senior level in Hobart a fortnight ago, quickly took control of the second set, though Robson continued to offer firm resistance.

Robson and Stephens have known each other since their days on the junior circuit and are good friends, as are their mothers. Stephens' mother texted her daughter after the match and passed on a message from Kathy Robson saying: “Great job and good luck in the next round.”

Asked about Robson's future potential, Stephens said: “She can be awesome. She has unbelievable timing. She's an awesome girl. She's pretty. I mean, what more do you want?”

With tongue perhaps only slightly in cheek, Stephens added: “I don't think we'll play that court ever again. We're turning into the Fed/Nadal rivalry.”

Murray, who was also troubled by a stiff shoulder in the first set, was too good in every department for Berankis, though the 22-year-old Lithuanian showed why he has long been regarded as one of the best young players. A former world junior No 1, he is a stylist with a fine repertoire of shots, though at 5ft 9in he lacks the power which has become such a factor in the modern game.

Although Murray was below his best, he has not dropped a set in his first three matches. He said that the plight of his best friend, Ross Hutchins, who is being treated for cancer, was an added incentive to do well. “I'll continue to fight as hard as I can this week to give him something to support and smile about,” he said.

Murray next plays Gilles Simon, who beat his fellow Frenchman, Gael Monfils, 6-4 6-4 4-6 1-6 8-6 in a remarkable match which finished at 12.40am after four and three-quarter hours and featured many ridiculously long rallies, including one of 71 strokes. Simon, who has lost his last nine matches against Murray, looked a physical wreck by the end.

Meanwhile two of the bigger threats in Murray's half of the draw fell by the wayside. Juan Martin del Potro and Marin Cilic were beaten by France's Jeremy Chardy and Italy's Andreas Seppi respectively. Chardy and Seppi now meet in the fourth round, the winner to face Murray or Simon in the quarter-finals.