Ash Barty has beaten doubles partner CoCo Vandeweghe 6-4 3-6 7-5 in the opening round of the Pan Pacific Open in Tokyo.
It was only a week ago that Vandeweghe and Barty combined to become US Open Women's Doubles Champions as they defeated second-seeded Timea Babos and Kristina Mladenovic 3-6 7-6(2) 7-6(6) for their maiden Grand Slam.
So the match had been dubbed the "Battle of the Doubles".
"It is always difficult playing friends especially straight after," Barty said after the match.
"It is always tough playing CoCo, we respect each other to play as hard as we can and the best person at the end of the day will come out on top," she said.
The pair had only faced each other once before which came in November 2017 where Vandeweghe took a straight sets victory. However, despite this victory, Vandeweghe had not gone past the first round in the last six tournaments she had played heading into the match.
Vandeweghe broke Barty twice in the opening set after some uncharacteristic faults but Barty was soon back in the match with an early break in the second set.
It came down to a third and final set. Each game was going to the server until Barty broke Vandeweghe at 5-4 but failed to serve it out and the game was level at 5-5. However, Barty broke Vandeweghe's serve and eventually took the match.
"I didn't serve it out the first time so that was disappointing," Barty said.
"I knew had to be clear and aggressive, play my game and get those last couple of points," she said.
Barty will face the winner of Victoria Azarenka and Kurumi Nara who play later today.