Coco Vandeweghe was in two minds whether to answer the call when an unknown number with a strange international dialling code popped up on her telephone last year.
Luckily, she said, she answered it rather than do what she normally does and divert it to voice mail.
Turns out the call was from former world number one Martina Hingis. And she wanted to know if she would play doubles with her at the tail end of 2016, including at the US Open.
"I was thinking 'who the heck is calling from this foreign number' and I usually don't answer my phone," the 25-year-old said courtside after she beat Eugenie Bouchard 6-4, 3-6, 7-5 to advance to the fourth round of the Australian Open singles.
"I could have sent Martina straight to my voice mail and that would have been the highlight of my career."
As it transpired Vandeweghe went even further -- she turned down Hingis, who has won five grand slam singles titles and 12 doubles titles.
Vandeweghe had already committed to playing both the Cincinnati and US Open tournaments with other people and she did not want to let them down.
So the answer was thanks, but no thanks. Until she had a conversation with coach Craig Kardon.
"I told my coach 'hey Craig guess what? Martina just called me' and he was like 'which Martina?', because he used to coach Navratilova and I said 'no Hingis, Hingis called me'," Vandeweghe added.
"I told him that she asked me to play doubles and I told her 'no', he said 'What? Are you kidding?'".
Vandeweghe did not require much more convincing and after contacting the two other players she had committed to play with, she and Hingis made the final in Cincinnati and then the semi-finals at Flushing Meadows.
They played twice more in Wuhan and Beijing last year and then teamed up in Sydney before the season-opening grand slam, making the quarter-finals.
The fifth seeds beat Jelena Jankovic and Yanina Wickmayer in the first round and are scheduled to play Australia's Ashleigh Barty and Casey Dellacqua in the second round, though Vandeweghe was mindful of the effect the two hour, 21 minute match against Bouchard might have on her.
"I think Martina is pissed because... I played just a bit too long to be fresh for the doubles," the world number 35 in singles said with a grin.
"But the first thing is to recover and be prepared as possible."