Updated

By Greg Stutchbury

MELBOURNE (Reuters) - Marin Cilic advanced to his first grand slam semi-final after the Croat resisted a dogged fightback from an injured Andy Roddick to edge their Australian Open quarter-final 7-6 6-3 3-6 2-6 6-3 Tuesday.

Roddick struggled with a shoulder injury he picked up in the first set and despite needing medical treatment throughout the second, the seventh seeded American battled bravely to take the match into a deciding set.

Cilic's previous best performance at a major was in reaching the quarter-finals at last year's U.S. Open and the 14th seed will next meet either defending champion Rafa Nadal or fifth seed Andy Murray for a place in the final.

"It wasn't easy. I got experience of it during the week," Cilic said in a courtside interview of having to play his third five-set match of the tournament.

"I just had a few extra gears in the last set.

"It wasn't easy when he started to play a lot better. I really struggled on my serve and he put a lot of pressure on me and I didn't know what to do.

"But I just took it point-by-point... and then I got the break."

The 27-year-old Roddick, meanwhile, will be left to rue the timing of the injury and was heard telling the trainer that his right shoulder felt "dead" and there was tingling in his hand while receiving treatment.

INJURED SHOULDER

Cilic edged the first set in a tiebreak and seemed to take full advantage of Roddick's growing fragility in the next, before the Croat had a nasty scare when he crashed into a line judge in the back court, though neither he nor the official were injured.

He regained his composure to secure the crucial break in that fourth game and held on to the advantage to seal the second set.

Roddick, however, came out firing in the third set and raced to a 3-0 lead as Cilic, who had beaten Juan Martin Del Potro in the fourth round in a five-set marathon, appeared to wilt and the American took it 6-3.

The American again started strongly in the fourth, racing to a 5-0 lead and while Cilic broke and then held, Roddick ensured the match would go to a decider.

The loss of those two games at the end of the fourth, however, served as a portent for the fifth with Roddick's momentum evaporating and Cilic raced away to a 5-2 lead.

He converted that advantage into victory two games later when Roddick's backhand push went wide, prompting the tall Croat to sink to his knees in celebration after three hours and 50 minutes.

(Editing by John O'Brien)