Konta battles past Tomljanovic in Brisbane after Muguruza pulls out

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Johanna Konta battled back from a set down for the second match in succession to reach the quarter-finals of the Brisbane International, as top seed Garbine Muguruza was forced to withdraw.

Born in Sydney but a British Davis Cup player, Konta needed three sets to get past surprise US Open finalist Madison Keys in the opening round of the WTA Premier event.

And it was a similar story at Pat Rafter Arena on Tuesday, the fifth seed overcoming Ajla Tomljanovic, a Croatian-born, naturalised Australian, 4-6 6-1 6-4 in two hours and 28 minutes.

A slow start saw Konta broken four times in the opening set alone, but she dropped serve just once more throughout, sealing victory with her first match point when world number 18 Tomljanovic sent a forehand return long. 

"It was a tough match, Ajla came out playing well in that first set, she made it very difficult," Konta, who will face either Ana Konjuh or third seed Elina Svitolina next, said in an on-court interview.  

"There wasn't a lot in it, I'm very happy to come through that. I didn't start off the way I wanted to, that's part of tennis. Credit to her. 

"It's a great thing to have two tough matches so early on."

Earlier, Muguruza had to quit in the third set of her match against Aleksandra Krunic due to cramps.

The world number two had led 7-5 6-7 (3-7) 2-1 when she pulled out.

As a consequence, Krunic advanced to a quarter-final against seventh seed Anastasija Sevastova, who eased to a 6-2 6-1 win over Sorana Cirstea.

Alize Cornet, runner-up to Karolina Pliskova in last year's final, defeated veteran Mirjana Lucic-Baroni 6-1 7-5.