An England victory by any margin would secure a first Grand Slam triumph in a decade, while a defeat by six points or fewer would still be enough to seal the title.
Wales started this campaign with a disappointing home defeat against Ireland but have since built up some momentum with wins against Scotland, France and Italy.
And Lancaster has warned his under-performing stars they must find a new level if they're to defeat an in-form Wales side on their own turf.
"I don't think there's any doubt about that," he said. "At half-time, we weren't quite accurate enough but still felt we were in control.
"We let that slip in the second half and Italy pushed us right to the end.
"We'll have to improve. Our accuracy overall wasn't quite good enough where it needed to be.
"I thought we were good in a lot of areas but not our accuracy with that final pass.
"We're delighted to get the win and relieved because of the pressure they put us under in the last 15 minutes."