Asked later why her relationship with Cahill - the former coach of Lleyton Hewitt and Andre Agassi - works, Halep said: "He knows how to talk to me when I need (advice). he just calms me down and it's flawless". A big forehand victor gave her the break for 3-1, and Keys continued to dominate on serve to take the opening set in just 22 minutes.
Halep had too much for Keys, making her tournament debut, and the Romanian said: "I think I played exactly what I had to play against her". "It's a good start to the tournament like this, where you knew you had to play your best to win".
Still a relatively new experience, the 28-year-old German reached the peak of the women's game last month after landing her second Grand Slam title of the year at the U.S. Open, capping a stunning season for the left-hander from Bremen.
Meanwhile, Angelique Kerber was given a harsh reminder of the pressure she faces as the new world number one when she was pushed to three sets before winning her opening match at the WTA Finals against Dominika Cibulkova on Sunday. Kerber's draw doesn't offer any relief either: She trails Simona Halep 3-4 in the head-to-head and has split her eight meetings 4-4 with Dominika Cibulkova. Halep has now won 14 of her last 20 sets played and is playing with extreme confidence at the moment.
In the third, Cibulkova was temporarily in charge with a 2-0 lead, but lost five of the next six games to end up on the losing side of the result. "Angelique has had a good year and won two major titles-the 2016 Australian Open and the 2016 US Open", said Colm McLoughlin, Executive Vice President & CEO, Dubai Duty Free. (Cibulkova and Halep would play for second place Thursday).
Kerber is guaranteed the year-end number one ranking after Williams pulled out of the $7 million season-ending WTA Finals in Singapore, which starts on Sunday, with a shoulder injury.
Halep quickly wrestled momentum away from Keys in the opening set, and a coaching timeout in the second was unable to help the Finals debutant turn things around as her opponent turned the screw. She's very strong on her legs. "I was focused. Everything went as I wanted, so I'm happy". Halep is 4-1 against Kerber on hard court.
In 2015, she was in the top 10 for the fourth time in her career, but no one, not even she, expected that in 2016, she would rocket to the top of the world rankings and win her first two Grand Slams. "I know her pretty well, so it's going to be a tough one".
"There is always a little bit more pressure when you really have to defend a big title, a lot of points", Radwanska said.
There was no sign of the battle that was to come when Kerber broke Cibulkova in the opening game and comfortably held her own serve but the seventh-seed clawed her way back and forced a tiebreaker.