MELBOURNE (AFP) - Three-time runner-up Andy Murray rode his luck to fight back and win a titanic four-setter over Grigor Dimitrov and reach the quarter-finals at the Australian Open on Sunday.

The sixth seed beat the 10th-seeded Bulgarian 6-4, 6-7 (5-7), 6-3, 7-5 and will now play Australian teenager Nick Krygios in the last eight.

The British star showed fantastic fighting qualities to claw back from 2-5 down in the fourth set to deny Dimitrov taking the epic match into a fifth and deciding set.

Murray, a two-time Grand Slam champion but luckless in Melbourne in three losing finals, will now have to battle a home crowd when he takes on Kyrgios in the last eight on Tuesday.

The Scot hit 42 winners and served at 67 per cent, breaking Dimitrov's serve seven times. "I got quite lucky at the end, a couple of net cords went my way and that was the difference really," he said of the gruelling 3hr 32min match on Rod Laver Arena.

Murray won match point on a net cord.

"A lot of the games were close, back and forth, and the momentum was switching both ways all the time," he said.

"Grigor is an unbelievable athlete, he's extremely quick around the court, so agile, and he gets shots that other players don't get to and he's got fantastic hands as well.

"I'm just glad that I managed to get through it at the end."

In the women's draw, Romanian third seed Simona Halep battled through to the quarter-finals with a hard-fought straight set win over unseeded Belgian Yanina Wickmayer.

She downed the world No. 80 6-4, 6-2 to set up a final-eight clash with Russian 10th seed Ekaterina Makarova.

"It was a very tough match but great. I played really well," the 23-year-old said. "I just wanted to go on court and be aggressive and focused because she's beaten me in the past."

Halep, a quarter-finalist at Melbourne Park last year, faced a stern challenge from Wickmayer, a former world No. 12 who reached the US Open semi-finals in 2009.

She dug in for a win, putting the result down to experience gained last year when she also reached the final at Roland Garros and the WTA Finals Singapore and the last four at Wimbledon.

The nuggety Romanian expected to improve against Makarova, who she defeated in their only previous meeting at New Haven in 2013.