Wales finished top of Pool D in Japan with four wins from four to set-up a clash with France, but full-back Williams knows how tough a test it will be.
“It’s been good so far. Topping the pool is exactly what we aimed for at the start of the campaign,” he said.
“We’re happy with four from four, but it doesn’t mean anything unless we beat France.
“They are a great team. We have beaten them seven out of the last eight times, but I think this is the biggest one. France have been playing well in this World Cup.
“It is going to be a tough one on the weekend. The boys are obviously really excited.”
France finished as runners-up in Pool C having beaten Argentina, USA and Tonga.
Their final group stage clash with England scheduled for Tokyo was cancelled due to the impact of Typhoon Hagibis.
“I think France have been playing really well,” said Williams, 28, who has two World Cup tries to his name in Japan against Georgia and Fiji respectively.
“They have got some old heads in their team and a lot of experience as well. We will go on to the training pitch this week and work on the stuff we will need to beat France on the weekend.”
The Wales camp are rightly wary of the French side and the dangers they bring.
But Williams, who had an excellent Six Nations as Wales claimed Guinness Six Nations Grand Slam glory, is hoping to take Gatland’s men all the way in Japan.
“I wouldn’t say we’ve got the easy route to the World Cup,” says Williams, “but we’ve got France next and we need to beat them to be looking at the bigger picture.”
