Grand Slam king reveals four-point plan to extend career.
Venus Williams is also drawn into the hard-hitting Red Group in Singapore
In a Twitter Q&A, Aussie No. 1 offers views on Mirka Federer, playing doubles with Andy Murray and more.
The Czech says he has suffered back pain since Wimbledon.
The Dutch-Swedish duo will make their first appearance at the WTA Finals.
The Oakland native is flying his San Rafael coop.
The Aussie had some highs and lows in 2017.
