The Champions League-winning Blues were easily beaten by the Europa League holders in Monaco on August 31 but young winger Bertrand insists that result will certainly not be repeated anytime soon.
"I think it was just a one-off. We're not looking into it too deeply," he told the club's official website.
"We're really disappointed that we couldn't top it off [the Champions League success] and go and win that cup as well, but it's important we just focus on the league now.
"We've been fantastic in that, with three wins out of three, so we just need to forget that bad result."
Chelsea will be looking to make it a 100% winning start to the Premier League season when they meet QPR at Loftus Road tomorrow.