Rafael Nadal`s drive towards a second Australian Open title came to a shuddering injury-induced halt Wednesday on a day of upsets that saw unseeded Kyle Edmund and Elise Mertens make the semi-finals. The world number one retired against Marin Cilic after an upper right leg problem began troubling him 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 number four 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 ground strokes in an intense battle. Romania's Halep plays her quarter-final against sixth seed Karolina Pliskova on Wednesday. Wozniacki last made the semi-finals at Melbourne Park in 2011 and she faces a familiar foe late Tuesday in Suarez Navarro, whose two wins in seven career meetings with her were both on clay.