MELBOURNE (AFP) - Rafael Nadal's drive towards a second Australian Open title came to a shuddering injury-induced halt on Wednesday (Jan 23) on a day of upsets that saw unseeded Kyle Edmund and Elise Mertens make the semi-finals.
The world No. 1 retired against Marin Cilic after an upper right leg problem began troubling him in the fourth set on Rod Laver Arena, with the Spaniard wincing in pain and limping as he struggled to continue.
His 3-6, 6-3, 6-7 (5-7), 6-2, 2-0 exit set up a last-four clash for the former US Open champion against Britain's Edmund, who stunned third seed Grigor Dimitrov 6-4, 3-6, 6-3, 6-4.
Mertens, who is yet to drop a set, was equally convincing in blasting past world No. 4 Elina Svitolina 6-4, 6-0 to become the first Belgian to make the semis since Kim Clijsters in 2012.
She will play second-seeded Dane Caroline Wozniacki or veteran Spaniard Carla Suarez Navarro for a place in Saturday's final.
Little separated Nadal and big-hitting Cilic until the injury struck, as they traded ferocious groundstrokes in an intense battle.
But the Spaniard, who was beaten in last year's final by world No. 2 Roger Federer, called the physio at 1-4 in the fourth set and again at the changeover when two sets apiece, and the writing was on the wall.
"It was an unbelievable performance from both us," said the sixth-seeded Croat. "It is really unfortunate for Rafa to finish this way."
It marked the second time Nadal has had to pull out with injury in Melbourne after calling it quits in the third set of his 2010 quarter-final against Andy Murray with a knee problem.
The look on Nadal's face said it all as he came to terms with missing a big opportunity to go after his 17th Grand Slam title after looking impressive in his early round matches.
"Tough moments. Is not the first time an opportunity that is gone for me," he told reporters.
"I am a positive person, but today is an opportunity lost to be in the semi-finals of a Grand Slam and fight for an important title for me.
"This has already happened to me a couple of times in this tournament and it's really tough to accept, especially after a tough December when I missed starting the season in Abu Dhabi and then Brisbane."
Nadal went into the year's opening Grand Slam tournament with knee concerns, but ironically, that wasn't the problem that finally brought him undone in the heat of battle with Cilic.
"I was playing okay. I was playing a match that anything could happen: could win, could lose. He was playing good, too," Nadal said.
"But I was fighting for it. I was two sets to one up. Yeah, just have to accept, recover, go back home, stay with my people and keep going. That's all."
Nadal said his problem was not hip-related, but more a muscle issue high up on his right leg.
"I can't tell you exactly the muscle. It's high on the leg. Tomorrow, we're going to communicate what's going on after a MRI scan," he said.
"Now is not the moment to say what's going on because we really don't know and the doctors really don't know yet."
Nadal said Tour organisers had to do something about the growing number of injuries among players after the withdrawals of Murray and Kei Nishikori before the tournament and Novak Djokovic struggling ahead of his exit on Monday.
"Somebody who is running the Tour should think a little bit about what's going on. Too many people are getting injured," Nadal said.
"I don't know if they think a little bit about the health of the players. I don't know if we keep playing on these very hard surfaces what's going to happen in the future with our lives."
Nadal said he was having no problems with the knee that forced him out of lead-up tournaments in Abu Dhabi and Brisbane.
"I was playing three hours (and) 50 minutes the other day. Today I was playing over three hours. I was running quite well."
Nadal's retirement follows the departure on Monday of Djokovic, with his immediate playing future uncertain after an elbow injury flared. The former world No. 1 also appeared to have a hip problem during his last-16 defeat to South Korea's Chung Hyeon.