Bertens: I was okay on the couch!

Kiki Bertens admitted she was quite content sitting on the couch before making a stunning start to the WTA Finals when she was called in as a last-minute alternate.

The Dutchwoman replaced Naomi Osaka after the Japanese injured her shoulder and swiftly made an impact in the Red Group, defeating world number one Ashleigh Barty.

It was a fine display from Bertens in Shenzhen as she battled from a set down to triumph 3-6 6-3 6-4, securing a first win over Barty at the sixth attempt.

"I was okay sitting on the couch," she laughed when asked about her whirlwind day on Tuesday.

"I was really tired. But then yesterday I just hit for five or 10 minutes. I just rested completely. I think today I felt already much better.

"Of course, it's not like after one day that you're completely back in full energy. As the match was continuing, I felt better and better.

"The movement was getting a bit better. I was starting to feel the court. I could play a little bit more aggressive, come to the net."

What an effort from Kiki Bertens. Has played every week since US Open, arrived in Shenzhen @WTAFinals on Monday after playing the Zhuhai final, gets the call to replace Naomi Osaka, cames back from a set and a break down to beat No.1 Barty. How: https://t.co/BzoQFVboHZ pic.twitter.com/4l4ULXKBdS

— WTA Insider (@WTA_insider) October 29, 2019