SYDNEY Swans defender Lewis Roberts-Thomson says a brief defensive lapse cost his side dearly in Saturday night’s 23-point loss to Collingwood at ANZ Stadium.

The Swans had kept the Magpies’ forwards to just nine goals in the first three quarters but Leon Davis broke the game open with three goals in the final term.

Roberts-Thomson and fellow talls Ted Richards and Heath Grundy kept the likes of Travis Cloke and John Anthony quiet but it was to no avail.

“We worked pretty well as a unit but you can’t let your guard down because Collingwood, no matter what player it is, they’re all very dangerous forwards who can kick a couple of goals.

“It just shows that you lapse five minutes and someone bobs up with two or three goals.”

More than 41,000 fans turned out for the mid-season blockbuster and Roberts-Thomson said it was disappointing that the Swans weren’t able to provide a better result.

“We understood that Collingwood set themselves up for this game and we’re sort of a barometer for them leading into the back half of the season and we treated the game the same way,” he said.

“We felt that Collingwood were a strong side. We have a lot of respect for them and we wanted to really match it with them but unfortunately they just ran away with it.”

The Swans travel to AAMI Stadium to tackle a rampant Adelaide next week in a bid to keep their stuttering finals hopes alive.

Another loss would leave the Swans needing seven wins from their last nine games – a tough ask for a team that has managed just five victories from the first 12.

Compounding matters is the Crows’ strong recent record against the Swans. Neil Craig’s men have won nine of the past 10 fixtures between the two sides.

However, Roberts-Thomson said he and his teammates would head into the daunting clash with optimism.

“They’re coming off the bye, too, so they’ll be refreshed and ready to go,” he said.

“But I think tonight, we’ll take plenty of positives out of it. There were some passages of play which were pretty exciting and really positive, so there’s a lot to learn and hopefully we can move forward from that game.”