Kei Nishikori
Nishikori's tireless work ethic saw off the challenge of Stanislas Wawrinka. Getty Images

Kei Nishikori outfought an off-colour Stanislas Wawrinka to claim an opening round robin win at the ATP World Tour Finals at The O2 Arena. Nishikori won 6-2 6-3 over the US Open champion, who produced an error-strewn display during a contest which lasted just 67 minutes.

Thirty-one unforced errors flowed from the racket of Wawrinka and ensured that Nishikori, who is chasing a place in the world's top three this week, eased to victory in the English capital. Two breaks came in the first set for the Japan number one, before the second set saw him complete the most comfortable of wins.

"Today I was very solid from the first game and very confident and it wasn't easy against Stan," the 26-year-old said. "I tried to play solid and I played a good match today. It is great to see a lot of support and this is a great atmosphere and I love to play here. I hope I can keep playing like this.

"[Reaching world number three] that is my goal for this week, to win as may matches and try and reach number four or number three. I see the opportunity to go up the rankings. I've been playing well this year and I shall try to keep it up."

New world number one Andy Murray and Marin Cilic will attempt to match Nishikori's victory in the other match in the John McEnroe group when they face-off on Monday [14 November] evening. The clash is the first match since Murray replaced Novak Djokovic at the top of the ATP rankings.

In the absence of Roger Federer and Rafael Nadal, former tournament semi-finalists Nishikori and Wawrinka had good reason to believe they could involve themselves in the shake up for silverware in London. Murray and Novak Djokovic's tussle for world number one had dominated the build-up to the event, but both of these players had made a living out of upsetting the applecart.

In front of a sub-standard crowd for the second day of competition, it was Nishikori who settled quicker but long forehands in the opening game prevented him grabbing an early break. Wawrinka was struggling to find his range and was eventually broken by Nishiskori after he swatted away a forehand.

Nishikori doubled his advantage via two double-faults in game seven from Wawrinka, allowing him to take the opening set with ease. The former US Open runner-up was combining baseline defence with the occasion foray to the net and it was proving too much for the Swiss to cope with.

Wawrinka did threaten a revival early in the second set as his backhand finally began to tick but Nishikori's metronomic form from the back of the court continued to be a thorn in the side. The world number five outfoxed Wawrinka with a floated service return which claimed the critical break, and from that moment the three-time grand slam champion unravelled.

The US Open winner was now visibly frustrated with his predicament with serves being rushed and groundstrokes being shanked, and that helped Nishikori complete a routine win in a little over an hour to see him top the group, before Murray and Cilic complete the opening round of matches.