Stan Wawrinka believes "everything went wrong" as he was convincingly beaten 6-3 6-2 by Rafael Nadal in his ATP World Tour Finals opener at the O2 Arena.
The out-of-sorts Swiss made 35 unforced errors and was broken four times as Nadal comfortably wrapped up his 14th straight-sets win in 17 meetings against the French Open champion.
Wawrinka admits he did not produce his best and hopes to make up for the disappointing opening display.
"When something went wrong today, everything went wrong. Just everything went the wrong way. Simple," he said, via the BBC.
"It was just a really bad day at the office. For sure, if you look, it's a really bad match. Bad behaving on the second set, going too fast. Things that are not too great on myself.
"Hopefully I can put it back together and get ready for the next match. It's the last tournament of the year, so I don't want to leave this week. I want to stay as much as possible."
The world number four will meet David Ferrer in his next group match on Wednesday.