Nitto ATP Finals 2018

Six-time former champion Roger Federer hits Centre Court at The O2 on Thursday ahead of the Nitto ATP Finals.

Marin Cilic strikes a backhand on Thursday in an early training session at The O2 ahead of the Nitto ATP Finals.

Five-time former champion and 2018 year-end No. 1 Novak Djokovic trains at The O2 on Thursday with Kevin Anderson ahead of the Nitto ATP Finals.

First-time qualifier Kevin Anderson trains with five-time former champion Novak Djokovic on Thursday ahead of the Nitto ATP Finals.

Kevin Anderson and his wife, Kelsey, take a boat ride to The O2 in London on Thursday ahead of the Nitto ATP Finals.

Alexander Zverev trains with his coach Ivan Lendl on Thursday in London ahead of the Nitto ATP Finals.