A thigh strain kept Farrell out of Sunday's 18-11 victory over Italy, when Toby Flood produced an excellent kicking display in his 56th international appearance to land all six penalties.
But when Lancaster came to name his team for a game certain to be played in a cauldron of noise - most of it fervently anti-English - he opted for the youngster with ice in his veins.
"He is a big-game player and he's really looking forward to it," the coach said of Farrell, who made his debut at centre in the first game of Lancaster's regime at the start of last year's Six Nations.
After subsequently vying with Flood for the flyhalf shirt, he made it his own last year when he produced a masterful display against the All Blacks, going toe to toe with Dan Carter and coming out on top as England chalked up a memorable win.
Farrell is not a flashy, eye-catching 10 but he has become ruthlessly efficient in his distribution and decision-making. His goal-kicking is out of the top drawer and he tackles with the weight of a dump-truck.
"The bigger the occasion, the more he likes it," Lancaster said of a player who inherited much of his no-nonsense approach from his father Andy, the current England assistant coach who captained the Britain rugby league team at 21.
Farrell junior always seems faintly bemused when asked questions about his temperament, as if it never crossed his mind there could be another way to approach things.
"It's all about composure," he told reporters at England's plush, training base in the Surrey woodlands, light-years from the Wigan base where he grew up.
"All I do is concentrate on my job. If I don't, I'll get found out. In a game like Saturday's it's about who concentrates for 80 minutes.
"You can't get lost in the occasion. A lot of players say big games go past quickly because they get caught up in it all.
"We'll take in the atmosphere when we walk out and when the final whistle's gone but for the match we'll just focus on the plan."
Farrell is often described as nerveless but laughed off the suggestion.
"I always get nervous before a game," he said. "You think about it so much you can end up playing the game three times in your head before you've stepped on the field.
"You have to try to move away, not beat yourself up before you've even played. Then, once you're out there, it's just a game of rugby."
Farrell, like most of his England team mates, has never played at the Millennium Stadium and even the few who have have never done so with a Six Nations championship on the line.
An eight-point win for the Welsh would give them a second successive title but England have their eyes set on nothing other than a grand slam.
"To be in this situation from where we were at the start of last year's Six Nations, well it's a credit to the staff and everyone involved as we've come on leaps and bounds and played some good stuff this year," Farrell said.
For all the talk of the "Cardiff factor" the statistics tell a different story. Wales have lost their last five games there, while England have won all four away games they have played in the tournament under Lancaster.
"We've taken steps forward this year, irrespective of what happens on Saturday," said Farrell.
"I feel the more we're together, the more people talk, the tighter we get. Everyone involved pushes each other, in a good way, and it's a brilliant place to be at the moment."
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