Defending champion Roger Federer eased into the quarter-finals of the Dubai Open on Thursday with a 6-3, 6-4 win over Spain's Tommy Robredo.

Paradorn Srichaphan joined the list of ousted seeds after his was knocked out by Croatia's Ivan Ljubicic, who beat him 7-6, 4-6, 7-5 in a draining second round tie.

Robredo competed well against the world number one, rallying furiously from the baseline and striking some fine passing shots. He was let down by his serve, however, which led to breaks in both sets.

"I thought I played pretty well today," said Federer.

"I was consistent and felt that even if he would come back I could control the match. That took pressure off my own serve. I served well again at the moments I had to, I played aggressive which is what I usually do on break points."

Robredo admitted he had been let down by his serve, but otherwise had few complaints.

"It's tough to play against Roger because he's playing at such a good level and all the time he's pushing you, but I played a great match in everything except my serve," he said.

"I couldn't put one first serve inside, and against the world number one it's difficult then. When I was playing at the baseline I was playing really good and I won a lot of the points."

UNFORCED ERRORS

Seventh seed Paradorn, suffering from a slight ankle injury, made too many unforced errors in the final stages of his match against Ljubicic after dragging himself back from the brink of defeat in the second set.

The Thai joins five other seeded players, out of a total of eight, already knocked out of the competition.

Neither player faced a break point in the opening set which Ljubicic sneaked 8-6 in the tiebreak when Paradorn put a backhand wide.

Ljubicic, who had reduced Paradorn to tears by beating him in the Thailand Open quarter-finals last September, continued to torment him with a serve that produced 17 aces.

The unseeded Croat broke to lead 4-3 in the second set, but Paradorn then called for the trainer and had an ice pack applied to his left foot.

When play resumed the Thai rallied to win the next three games and the set, levelling at 4-4 with a drop volley and striking a blistering crosscourt forehand winner to earn set point.

However, in the deciding set Paradorn appeared to tire in the heat and netted a forehand to drop the 11th game, allowing Ljubicic to serve out for the match.

"I tried to go for too much at the end and missed it," said Paradorn. "It was exactly the same as in Bangkok, 7-5 in the third and losing my serve at five-all. It was a very tight match and it could have gone either way."