Sydney coach Paul Roos vigorously defended key forward Barry Hall after his barren afternoon in Geelong's regulation 51-point AFL win over the Swans.

Hall was restricted to only five possessions, including none after halftime, gave away three free kicks and only kicked 0.1 in Saturday's 17.14 (116) to 10.5 (65) loss to the unbeaten Cats at Skilled Stadium.

Roos said Hall had no chance to be a factor in the game because the Swans used the ball so poorly.

"I can't even think of a one-on-one contest after halftime that Hally and Scarlett were involved in," Roos said of Hall's duel with star Cats defender Matthew Scarlett.

"With all due respect to Scarlett, it was probably an easy day for him after halftime because he really didn't have to do anything.

"We tended to go to Hally with three guys on him and he was never going to mark those.

"The concern is less about him getting no ball and more the result of poor decision making and poor skill execution .... I'm not concerned about Hally at all."

Cats coach Mark Thompson also conceded the way Geelong controlled the game made it very tough for Hall.

"The way we played, it would have been hard for Hall to score today and obviously Matthew is one of the best defenders to have played the game - and he got a lot of help from his teammates," Thompson said.

The Swans restricted Geelong to only one goal in the opening term as the Cats kicked into a swirling breeze.

But by early in the third term the home side had blown their lead out to 34 points.

Swans midfielder Adam Goodes then had a purple patch, kicking two goals as Sydney reduced the margin to 15 points, before Cat Harry Taylor made a superb spoil in the middle of the ground and set up a goal that took any pressure off his team.

"When we started to get a bit of momentum, we gave them a goal and it just completely took the momentum away from us," Roos said.

Geelong were missing their No.1 player Gary Ablett, who is sidelined with a groin injury.

But they did not miss a beat as midfielders Joel Corey and Joel Selwood dominated.

Steve Johnson also impressed in the first half with four goals.

"I was absolutely thrilled we were able to release the shackles and (put) on a bit of a score and end up kicking 100 points," Thompson said.

"We missed him (Ablett) ... (but) we still played well, we played Sydney exactly the way we planned to play them.

"We knew the start would be like that, it would be tight, but our boys just persevered with what we wanted to do and work on, we did it exceptionally well.

"To beat Sydney by 51 points at any time is a pretty good performance."

Roos said the Swans matched Geelong in many areas of the game, but their skill errors were too costly.

Goodes was best for the Swans while Michael O'Loughlin kicked three goals, including the 500th of his career.

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