ATP World Tour Finals Day 1

Nishikori bt Murray 6-4, 6-4

Andy Murray has slumped to a 6-4 6-4 defeat at the hands of Kei Nishikori in his opening match at the ATP World Tour Finals.

The British number one had been opening to mark his return to the event at the O2 Arena in London with a victory but he was second-best for much of his encounter with the Japanese.

Murray broke in the fifth game of the match to seize the early advantage, but that setback sparked Nishikori into gear and the US Open-runner-up dominated the remainder of the set to move ahead.

It was one-way traffic at the start of the second as Nishikori raced into a 3-0 lead, but after digging deep to avoid the double break, Murray fought back to 4-4 to give him the momentum heading into the critical part of the set.

However, like in the first set, Nishikori struck in the 10th game to break Murray's serve to seal the win on his debut at the tournament.

Murray will return on Tuesday aware that he needs his second match, against either Roger Federer or Milos Raonic, to give himself a change of progression to the semi-finals.

Federer bt Raonic 6-1, 7-6

Roger Federer kicked off his ATP World Tour Finals campaign in impressive style as the world number two stormed to a 6-1 7-6 victory over Milos Raonic at the O2 Arena.

The Swiss ace offered the London crowd a sign of what was to come in Raonic's opening service game by securing an early break of serve to pile the pressure on his rival.

Federer, who lost just five points on his serve in the opener, would need just one more break as he wrapped up the set in 25 minutes.

Raonic proved to be a more stubborn force at the other end of the court in the second set, despite being forced to save a break point at 1-1.

Federer was asked to save break points in successive service games, but he responded in emphatic fashion to close the door on his Canadian rival with a couple of perfect serves.

The set would continue with serve as both players missed chances to make the breakthrough, and it was Federer who produced his best tennis of the match to secure the win in the tie-break.

Raonic's decision to attack Federer would ultimately prove to be his downfall as a number of errors, including a double fault, handed the second seed a 7-0 win in the tie-break and victory on the opening night of the season-ending event.