Melbourne - Serena Williams said she was "almost relieved" to go tumbling out of the Australian Open Wednesday after injury turned her 50th Grand Slam appearance into the worst of her life.
Williams, who was targeting a calendar-year Grand Slam and aiming to become the oldest women's world number one in history, was stunned 3-6, 7-5, 6-4 by teenager Sloane Stephens.
After rolling her ankle in her first match and hitting herself in the mouth with her racquet in the second, the 31-year-old suffered back spasms in the second set against Stephens which limited her movement.
Despite momentarily considering retiring from the match, she led 4-3 in the final set before Stephens prevailed to reach her first Grand Slam semi-final at the age of just 19.
"Well, I was running to the net for a drop shot," Williams recalled of the moment she tweaked her back.
"As I went to hit it, it was on the backhand - I even screamed on the court. I was like, aagh. I totally locked up after that. It was a little painful.
"I've had a tough two weeks between the ankle, which is like this big every day, and my back, which started hurting. A lot of stuff. It was what it was."
The 15-time major champion said she had never endured a tougher time at a Grand Slam tournament, since making her major debut at the 1998 Australian Open.
"For a Grand Slam, absolutely," she said. "Oh my gosh, I'm almost relieved that it's over because there're only so much I felt I could do. It's been a little difficult. I've been thrown a lot of balls these two weeks."
Williams could only serve at about half-pace late in the second set and early in the third.
"At that point, you just have to pretend like nothing's wrong," she said. "You think of worst case scenarios. My legs were fine, so running was fine. Just rotating on the serve and backhand was tough."
Williams angrily smashed her racquet on the court while blowing the chance to claim the world number one ranking.
"Did you see it?" she said of her racquet-busting tantrum. "I even had a wry smile on my lips after that. It made me happy, unfortunately."
On the top ranking, which she can still claim if Victoria Azarenka and Maria Sharapova both lose in the semi-finals, Williams added: "I don't think about that so much.
"For me, I'm trying for Grand Slams and to win titles, to get to 50 titles. Number one is awesome if I get it. I think I'll get there one day. If not, I've had it, so it is what it is.
"But for me, it's definitely more about doing well in tournaments."