Stan Wawrinka admitted that his errors spiralled out of control during his straight set loss to Rafael Nadal at the ATP World Tour Finals on Monday.
The Swiss Ace would notch up 35 unforced errors during his 6-3, 6-2 loss to the former world number one on the hard courts of the O2 Arena in London.
"When something went wrong today, everything went wrong," quipped the French Open champion on the ATP World Tour website.
"It was just a really bad day at the office."
The world number four admitted that he would have to improve if he wants to make the semi-finals at the ATP's swansong event.
Waiting for Wawrinka in Group Ilie Nastase are world number two Andy Murray and Spain's David Ferrer.
"For sure I will have to play better, but you never know," added the 30-year-old.
"That's why it's interesting here, you can lose the first match, still qualify. I will have to play some better tennis."
Meanwhile, Nadal was happy with his performance against Wawrinka, picking up his second win over the Swiss for the year.
"I think I played a solid match," said the Manacor-native, who has battled his way back to world number five after a series of injuries.
"I had one bad game, the first one of the match. But then immediately I was playing well. I played the way that I wanted to play. I played aggressively. I played with not many mistakes."