Cilic serves notice he is to be taken seriously

A single break in the final set proved enough for the 14th seed to complete a 5-7, 6-4, 7-5, 5-7, 6-3 success over Juan Martin Del Potro in a match that lasted 4hrs 38mins.

A recurrence of a back injury forced Dinara Safina to retire against Maria Kirilenko yesterday.

Marin Cilic first announced that he was ready to be a serious contender among the top echelons of men's tennis when he trounced Andy Murray with a stunning display at the US Open last September. The Croatian proved that performance was no fluke as he ended Juan Martin Del Potro's hopes of a second successive grand slam title with an epic five-set victory in their fourth-round clash in Melbourne yesterday.

A single break in the final set proved enough for the 14th seed to complete a 5-7, 6-4, 7-5, 5-7, 6-3 success over the world No 4 in a match that lasted 4hrs 38mins. Cilic, who had lost to Del Potro at the same stage 12 months earlier, said: "I think since the US Open I've started to play much better and win against better guys more often. "I've had some tough matches here in the first few rounds, but today I felt really good physically, and that in the end was the main difference.

"I've played some great matches and winning against Del Potro shows that I'm not going to let it go easy." A magnanimous Del Potro said that the better player had won: "Marin is playing a great tennis. I think he did better than me and he won. "You know, after four hours, you have to focus. And he broke me very soon in the fifth. Then I had my chance in the last game. I missed a forehand." Del Potro is to return to Argentina and recover from nagging injuries that led to the trainer twice being called out to give him physio against Cilic.

"My whole body (is sore)," he added. "I will go home and I will see the doctors there. I need a little rest to recover and be in good shape for the next tournaments." Cilic, who is likely to move up towards a spot in the top 10 in the ATP rankings regardless of how much further he goes in the tournament, will face Andy Roddick in the quarter-finals tomorrow after the American defeated Fernando Gonzalez in a five-set thriller.

The No 6 seed looked to be in big trouble when he trailed by two sets to one to the in-form Chilean, but he rallied to triumph 6-3, 3-6, 4-6, 7-5, 6-2. Roddick said: "I was lucky to get out of that. I took Fernando's best stuff for the majority of four sets. Sometimes if you stick around, you get your reward and that's what happened. "I got a little lucky tonight - and sometimes it's better to be lucky than good." [e-mail]