For all her brilliance and experience and that bloody-minded determination of a champion, there were two things Serena Williams simply could not overcome at Wimbledon on Monday.One was Round-of-16 opponent Sabine Lisicki, who produced the performance of a lifetime to clinch a stunning upset – 6-2, 1-6, 6-4.The other was age.Williams' astonishing form throughout 2013, good enough for a 34-match winning streak of imperious dominance, was such that she had begun to seem timeless. Yet it must be remembered that Williams is now 31 years old and the exception rather than the rule in what is increasingly a young woman's game.While all her advantages in terms of technique and power and court smarts are too much for most of her out-matched opponents to deal with, those capable and brave enough to stick to a certain plan may increasingly find positive traction against her.Lisicki was game to try to wear Williams down, confident she could stick around long enough for the American's legs and spirit to get weary.She moved Williams around Centre Court, attacking Serena's ferocious forehand with wide slicing serves and whipping groundstrokes deep into each corner.It was a tactic that looked ultimately destined to fail when Williams took a 3-0 lead in the deciding set, before Lisicki dug deep once more for a final revival that saw her reel off six out of seven games.At the end, Lisicki sunk forward to her stomach, sobbing in delight and disbelief at the finest moment of her career. The 23-year-old German reached the 2011 semifinals at Wimbledon, and this win continued her extraordinary streak of having beaten the reigning French Open champion at Wimbledon on four occasions.But nothing was bigger than this, a triumph over a living legend who was seeking to match the longest winning streak on the women's tour since the turn of the century. Serena's sister Venus Williams won 35 straight in 2000."I am shaking," said Lisicki. "I am so happy. Serena is such a tough opponent and it is an amazing feeling to win this match."Williams had no excuses and found some gracious words for Lisicki at the net and some more during her post-match press conference."It's not a shock," Williams said. "She plays really good on grass and has a massive serve. Sabine played really well, she always plays really well at Wimbledon."Every time I step on the court I am the favorite so I have grown to get used to that. You know it is not going to be an easy match against her. I need to do better. She played a super-aggressive game. When you have absolutely nothing to lose you can play with so much freedom and you can be so loose."At certain times in her career Williams' conditioning has been called into question, but that had nothing to do with this loss. All those years on tour might have taken a step off her speed, but throughout this year she has kept in exceptional shape.This was a defeat as simple as an inspired opponent and the cruel sands of time.Even after 16 Grand Slam titles Serena is not done yet, not by a long shot, though this was a reminder that in the coming months and years her age may be a tougher foe than most of her supposed rivals.