Danielle Collins overcame scorching heat to beat No. 19 seed Elise Mertens 4-6, 6-4, 6-4 at the Australian Open on Monday.
In match that lasted two hours and 51 minutes, the American 27th seed came from a set down to produce a series of power shots to eventually see off her Belgian opponent.
Mertens, who won the opening set, saved two match points in the third and deciding set before a double fault saw her lose out.
“I think I have my ups and downs during the matches, mentally and physically,” Collins said afterwards.
“Elise was really working me to the max. She’s one of the best anticipators on tour. So sometimes I was having to win the points five, six, seven times.
“Some of the points were incredible. Some of the balls she was getting back and shots I thought were winners, sometimes they weren’t.
“So I had to try to put some pressure on her and come up with some big shots because that’s all you can do against someone who is such a good anticipator.”
Collins became the third American to reach the quarter-finals this year, along with Jessica Pegula and Madison Keys and she will play either Simona Halep or Alizé Cornet for a semi- final spot.
Collins is still playing doubles and admitted it was tough
“I played a long match the other day against Clara Tauson for two and a half hours and then I played doubles, so I spent about five hours on court,” she said.
“I had to make a lot of technical adjustments to make myself comfortable moving around, especially serving.
“That was a big challenge and now I need to focus on getting ready for doubles again.”
