But they recovered and went the remainder of the tournament - 357 minutes - without conceding a further touchdown, a Six Nations record.
Wales withheld everything Grand Slam chasing England had to offer on Saturday and claimed a 30-3 victory over the old enemy - their biggest in history - to secure back-to-back Championships for the first time since 1979.
And defensive captain Roberts has paid tribute to his teammates' ferocious attitude and the work put in by defence coach Shaun Edwards.
"We're hugely proud of our defence," said Roberts.
"These Test matches are won by defence and I sincerely believe that if you stop a team scoring points and grab a few turnovers, the guys like Justin Tipuric and Alex Cuthbert are put in space and can win games.
"To concede just three points against a team of this potency is very, very good for us and a tap on the back to Shaun.
"From a personal point of view it's been an absolute privilege to work with him.
"He's a great character, he knows his stuff inside and out and to learn from someone of his calibre is up there with one of my greatest experiences as a rugby player. I can honestly say that.
"To see him smiling at the end is very pleasing. It's a successful defence of the Cup and it's very rewarding.
"It's a better buzz than last year if anything, because our games have been built on solid grunt and attitude and certainly the three on the road and this win over England.
"We took a bit of a beating from a lot of people after that Ireland game and certainly the run of results leading up to that.
"It was a very hard place to be. But it just goes to show the resilience of the boys. Rugby is 90% attitude and the resilience the boys have shown the last six seven weeks has come to the fore and it's very pleasing."
This season's tournament was dominated by defence and saw the least amount of tries in history.
Wales led the try-scoring stakes but Roberts insists there is still far more to come with ball in hand.
"There's more to come from us and that's the scary thing," said Roberts.
"Certainly from a backs point of view, to play in a game when you're not playing with a bar of soap, with a bit with ball in hand on a dry track with the roof closed, was nice to show what we could do as a backline.
"There is more to come. Certainly, Our defence is outstanding, there's more to come in attack."