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Centre Jamie Roberts admits he is "under pressure" to perform as Six Nations title-chasing Wales take on Italy in Rome on Saturday.

Scott Williams came off the bench for Roberts to score a try in the 23-16 win against Ireland, impressing head coach Warren Gatland.

Roberts, 28, says the competition to keep the number 12 shirt will spur him on against the Italians.

"I know if I don't perform the jersey will go to him [Williams]," he said.

"Scott is a wonderful player and he's having a great season so far.

"He came on [against Ireland] and played very well. That puts pressure on me and that brings out the best in me and making sure I perform for 80 minutes.

"I know there's lots of things I can work on in my game and yeah I have to be prepared for that battle for the jersey.

"Scott is certainly putting that pressure on at the minute....so that's keeping me on my toes."

Scarlets centre Williams has been named on the bench for the match against the Azzurri.

The match at the Olympic Stadium is followed by Scotland against Ireland at Murrayfield and England versus France at Twickenham on the final weekend of the Six Nations.

Wales need to win and overhaul their significant points-difference deficit compared with England and Ireland to lift the trophy.

Roberts says although scoring as many points as they can is important, they must not forget about their defensive responsibilities.

"Yes we have to score points," said the 2009 and 2013 British and Irish Lion.

"But for every point they [Italy] score, we have to score two.

"So the boys have to be on the money defensively as well as in attack.

"We just have to play the game in the right areas...play the territory game well...we just have to be very clever."