Andy Murray was at a loss to explain why he was always on the back foot as he went down to a miserable 6-3 6-1 defeat to Kevin Anderson in the Rogers Cup in Montreal.
The world number four was never in the match in which he served five double faults with his opponent, ranked 31 places below him, refusing to allow the Scot to settle as his attempt to defend his title disintegrated at the first hurdle.
The 25-year-old South African played with an intensity and aggression that prevented Murray from finding any rhythm, dictating play as he bossed the Scot around the court and growing in confidence as the match continued.
Murray saw his serve desert him and the match was scattered with unforced errors as he lost in an hour and 10 minutes.
It was a less than an ideal start to his build-up for the US Open which begins in less than three weeks in New York.
The 24-year-old could not put his finger on what was behind such a comprehensive loss after time spent preparing in Miami.
Murray said in quotes reported on atpworldtour.com: "Sometimes you can make mistakes with your preparation, but I've done pretty similar stuff to what I've always done coming in here. It's just a really bad day.
"It's happened to me a couple times this year and also last year, as well.
"I just felt very slow. I couldn't get anything going. I started both sets really, really badly which doesn't help against someone that serves like Kevin.
"Every time he came to the net, I was a bit late getting to the ball. I was getting behind very early in all of the rallies and didn't move particularly well."
A flying start by Anderson left Murray playing catch-up as the South African went in to a 3-0 lead, with the Scot serving up two double faults in his first service game.
Murray finally got on the board in the fourth game and the match went with serve before Anderson took a 5-2 lead.
The Dunblane-born player then held but it was merely delaying the inevitable, Anderson ending the set the way he started it, serving out with an ace.
Murray then began the second set with a double fault as Anderson was relentless, forcing his way to double break point and going 1-0 up before holding.
The Briton held but it was the final game he would win, producing double faults, unforced errors and generally poor play.
Anderson told Sky Sports 4: "Andy is a great player and has had an incredible career.
"I knew it was going to be tough.
"The last time I played Andy was in Australia and I didn't come forward very well.
"I knew I had to come in.
"I played some good points and I won the majority of those."