The defender says they were relying on their quality coming through in the 1-0 win over Sunderland.
The result at the Stadium of Light took them to eight games unbeaten in all competitions so far this season, as well as continuing their unbeaten record on the road during this campaign.
And Bertrand says that fine run of form has got confidence soaring at St Mary’s.
“There is (a lot of belief), especially with the results of late,” Bertrand told saintsfc.co.uk.
“It’s important we keep that consistency and keep that work ethic that we showed. Hopefully then the results will keep coming.”
The full back also admits that they knew things would be tough against Sam Allardyce’s side after their heavy defeat to Everton last weekend.
The Black Cats were thoroughly dismantled by the Blues in that 6-2 defeat, meaning they were more than keen to put in a big performance this weekend to rectify for that.
That was something they did as they held Ronald Koeman’s side at bay until a Dusan Tadic gave the away side all three points, and Bertrand says they were relying on their quality to shine through eventually.
“We knew it was going to be a tough place to come so it was important we dug in,” he added.
“We had to compete and then hopefully our quality would come through, which it did. It was a very tight game, but we were trying to create chances. Maybe our final pass let us down at times.”