The off-colour champions made to battle

Roger Federer and Maria Sharapova showed why they are champions at Wimbledon, when both continued the defence of their singles titles without playing their best tennis. Federer dropped his first set in this year's tournament but defeated Nicolas Kiefer 6-2 6-7 6-1 7-5.

The German stole the tie-break in the second set by taking two successive points on Federer's serve as he reeled off five points in a row. But the champion broke Kiefer in the first game of the third set and, despite dropping his serve twice in the fourth set, he stayed in overall control to take another step towards a third successive title.

"For me only the title would be satisfying this year, with the misses I've had at the French and Australian Open," said Federer, who lost to the eventual winner in both the earlier Grand Slam events this year. "We've played on several occasions and [Kiefer] beat me few times, once on grass. We know each other's game pretty well and at times you could see that because we took advantage of each other's game. I had to survive some tough moments.

I had the feeling I should have won in three but, in the end, I'm happy to win in four." Unbeaten on grass since Wimbledon 2003, Federer plays Juan Carlos Ferrero in the fourth round. The Spaniard beat Florian Mayer, another German, 3-6 6-2 6-1 6-1. Sharapova's infamous shriek was at top pitch and her fighting qualities needed to be, too, as she battled her way past Katarina Srebotnik 6-2 6-4 in a match that was closer than the scoreline suggests.

The Slovenian made Sharapova battle hard in several games, providing her with a useful test before the tournament heads into its second week. Her next opponent is Nathalie Dechy, of France, who defeated Alyona Bondarenko 6-1 6-4. "She has a great grass-court game and I know that every round will get tougher now," the Russian said of Srebotnik. "I could have served better at the beginning of games maybe and sometimes it lacked a bit of penetration. I got through this match without feeling great."

Lindsay Davenport, seeded ahead of Sharapova at No 1, is upset that the seeding committee was less flexible in the women's singles than the men's, with the result that the Williams sisters, Venus and Serena, who have both won the title twice, will meet in the fourth round. After beating Dinara Safina, of Russia, 6-2 6-1, Davenport said: "I don't understand the philosophy of, 'We're going to do this for the men, but we won't do it for the women'. As an American, it makes no sense."