GREATER Western Sydney star Ryan Griffen says his side failed to stand up to the pressure of last week's intense clash with Port Adelaide.

The Giants took on the Power for a chance to keep themselves in touch of the top eight, but came away with a disappointing 21-point loss in a game they could easily have won.

GWS were jumped at the opening bounce against Port, and although they managed to steady and lead at the final change, the Power kicked five goals to one in the last term to clinch the win.

Griffen says the visitors' poor start and failure to cope with the boisterous Adelaide Oval crowd cost them.

"It probably was a lost opportunity, (but) the boys had a crack," Griffen said on Tuesday.

"We didn't start too well but got back into the contest and couldn't quite get over the line.

"It's pretty hard over there, the atmosphere for Port Adelaide is unbelievable."

GWS take on the Swans in this week's Sydney derby with their season and finals hopes on the line, but will do so without co-captain Phil Davis.

The key defender has been ruled out for the rest of 2015 after injuring his hamstring in the first half against the Power.

The loss of Davis will no doubt mean a reshuffle for the Giants' defence, and Griffen says the loss of the skipper is a blow.

"He's been massive for us, he's had his ups and downs over the years but he was playing some consistent footy early for us," Griffen said.

"For him to go down, it hurts, but we'll have someone come in and cover him and hopefully we can play some really good footy this weekend.

"It's a do or die game for us if we want to make finals. I know the young boys want to get their first finals appearance, so we're looking to get a good result."

Griffen stood side by side at Tuesday's media conference with Swans star Josh Kennedy, and the pair will no doubt be reacquainted on Saturday at Spotless Stadium in the eighth Sydney Derby.

Kennedy is the clearance king at the Swans and is ranked second in the competition for contested possessions, so his role in the engine room will be crucial for his side.

While the visitors might have the edge in experience against the Giants, Kennedy said both he and his fellow midfielders knew the quality of players they would be up against.

"It's one of the strongest parts of their team and if we can get on top there and try and spend the majority of the game in our forward half, it will go a long way towards winning the game," Kennedy said.

"They've had an amazing year and they've got some quality players and we know that each year they've gotten better and are really competitive.

"They knocked off Hawthorn earlier in the year so from our point of view it's going to be a tough game as it always is, (and) very physical.

"They're really hard at it, (and are) a great contested ball team so there's a lot on the line.

"We want to get a top four spot and feel like we have to win every game from here to get that."