ROME -- Ireland made a scrappy start in defence of its 6 Nations title by labouring to beat Italy 26-3 on Saturday.

The visitors were in command throughout, but couldn't show it on the scoreboard until more than an hour passed. Even then, it took Italy to be reduced to 14 men for Ireland to finally produce a try.

Referee Pascal Gauzere tired of Italy's infractions and sin-binned hooker Leonardo Ghiraldini.

Within seconds, Ireland turned a 12-3 lead on penalties into 17-3. Captain Paul O'Connell's lineout grab was taken to the line by No. 8 Jordi Murphy, and scrumhalf Conor Murray dummied and barged over beside the ruck.

Ireland had the win in the bag, but for good measure, space opened for last-minute starter Tommy O'Donnell to run in a second try in two minutes.

O'Donnell started only because flanker Sean O'Brien, set to play his first test in 15 months after two shoulder reconstructions, injured his hamstring in the warmup. Ireland coach Joe Schmidt was "quietly confident" O'Brien will pass scans in Dublin.

If O'Brien was the worst of Ireland's problems, then the visitors could regard it as a good day, an eighth successive test win for the first time since 2009. The plague of knock-ons could be explained away by a first match in 11 weeks and a slippery field, all the while facing proud opposition who play their best at home.

"It was a slog, but I don't know if it was that frustrating. Any time you come to Rome that's exactly what you're expecting -- a slog," Ireland fullback Rob Kearney said. "We knew that if we just kept chipping away and trying to build some phases that eventually we would break them down."

Schmidt suggested Ireland's display was "between 30 and 40 per cent off" what England showed in a 21-16 win over Wales in Cardiff on Friday.

"I don't think we would have played with them last night," Schmidt said. "We certainly need to up our game. Part of it was the pressure Italy put on us but I know we can do better than that. ... We had six of the starting 15 we had this time last year. That in itself presents a challenge."

Until the burst of tries, both sides found the other's defence unbreakable, and resorted to kicking for territory. Italy lost four of its lineout throw-ins, and it was troubled by Ireland's rolling maul, but mistakes kept ruining any Irish momentum.

"The game probably went how a number of us expected it would," Schmidt said. "We didn't help ourselves too much but at the same time we got good field possession and the Italian defence was very hard to break down."

Flyhalf Ian Keatley kicked four penalties to one by Italy counterpart Kelly Haimona before the two converted tries made up Ireland's biggest win in Italy in six years.

Italy came closest to a try near fulltime, when Luke McLean's chip couldn't be gathered by captain Sergio Parisse, and ended up being grabbed behind the try-line by Haimona. But the try was disallowed by video replay, which suggested the ball brushed Parisse's fingertips, and therefore was knocked on.

But Parisse said he didn't touch the ball.

"We only had two or three minutes of interesting play, in the final minutes," Italy coach Jacques Brunel said.

"We showed great quality in the defensive phase. But ... it's impossible to win with so little possession. Certainly, the main issue today was the lineout. Our scrum is at or even better than Ireland's level."

But Italy knows it needs more than a good scrum to beat Ireland when they next meet, in the Rugby World Cup on Oct. 4 in London.

Next weekend, Ireland hosts France, while Italy visits England.

"If we go to Twickenham and play like we did today, only defending in the first half, it's going to be difficult," Parisse said.