The six-time champion comes into the tournament having reached the semi-finals of the Paris Masters recently which followed his 99th career title in Basel.
His defeat in Paris was against great rival and world number one Novak Djokovic in what was a stunning, closely-fought match so he will be feeling confident about his game as he kicks off his campaign in London.
The 37-year-old has faced Nishikori twice in the last month - in Shanghai and Paris - and on both occasions he was victorious in straight sets.
Nishikori will be making his third appearance at the finals and he has performed well on his previous two visits, reaching the semi-finals in both 2014 and 2016.
The Japanese star's form has been very consistent in recent months, as after reaching the semi-finals at the US Open, he has gone on to appear in two finals, another semi-final, and two quarter-finals.
Nishikori has not been able to find the answers to Federer's game in their two recent meetings so that may affect him mentally here so he must try and treat this meeting as a clean slate.
Two recent defeats to Federer will be fresh in Nishikori's mind but he did compete well in their Shanghai and Paris matches so he certainly has what it takes to test the six-time champion. He will hope that his opponent is suffering from a mental and physical hangover from his recent gruelling defeat to Novak Djokovic in Paris, but Federer has been in positive mood heading into London and will be fully focused on making a charge towards his 100th career title.
Nishikori is playing solidly at the minute and will compete well, but Federer is a level above and should get his first points on the board. Federer in straight sets.