Stan Wawrinka's hopes of reaching a fourth consecutive semi-final at the ATP World Tour Finals were dented by an opening loss to Kei Nishikori.
The third seed, who sported a poppy on his shirt, had never previously lost to anyone at the O2 Arena other than Roger Federer, Rafael Nadal or Novak Djokovic.
But he was well below his best and fifth seed Nishikori ran out a convincing 6-2 6-3 winner.
The victory boosts Nishikori's hopes of overtaking Wawrinka to finish the year as world number three, and he said: "That's my goal for this week, try to win matches and try to reach number four or number three.
"I've been playing really well this year so I'll try to keep it up. Today I think I was very solid from the first game and I was very confident. I thought I played a good match."
Nishikori next faces the winner of Monday evening's match between world number one Andy Murray and Marin Cilic.
Wawrinka led their head-to-head 4-2, winning their most recent meeting in the semi-finals of the US Open before going on to win his third grand slam title.
But, brilliant as he can be, the Swiss is also erratic and there were far too many errors in the opening set in particular.
Nishikori's movement was sharper and his ball-striking cleaner, and he earned his rewards with five games in a row to win the first set.
Wawrinka's struggles were rather summed up by two double faults to hand Nishikori a second break of serve, and the Japanese star clinched the set with a fine backhand volley.
His net play was a feature of the set, the fifth seed winning seven points with volleys.
Wawrinka tried to fire himself up at the start of the second set and initially played better, but he then misjudged a return that landed on the baseline and was broken in the fifth game.
The 31-year-old never looked like recovering and, when he drilled a backhand long after an hour and seven minutes, the match was over.
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here