Angelique Kerber said she was simply punished for an off-day after her Australian Open title defence ended at the hands of an inspired Coco Vandeweghe on Sunday.
Top seed Kerber was emphatically dumped out in the fourth round at Melbourne Park as world number 35 Vandeweghe delivered a superb display of power-hitting on Rod Laver Arena.
In a post-match news conference, Kerber said: "It was a tough match, and of course I'm disappointed. But I was not feeling the ball at all tonight. I was not playing good from the first point. It was not my day and not my match, for sure.
"I missed a lot and I made a lot of unforced errors. So this was not my game like I play normally."
Having failed to make the second week of her first grand slam as the world number one, Kerber is confident she can bounce back.
"I learned a lot, and I have new experience now. I mean, I'm looking forward to all the next tournaments that are coming," said the German.
"Of course, they are new experiences [defending the title and playing as world number one]. This is good, they are new challenges. I can learn from all the other stuff which is new for me.
"Let's see; it's just the beginning of the year. I can still improve my tennis, which is good. I will try my best to, coming back stronger."
Vandeweghe - a quarter-finalist at Wimbledon in 2015 - will go on to face Garbine Muguruza in the last eight.