Holders Wales got their bid for an historic hat-trick of Six Nations titles off to a nervy start when they squeezed past a dogged Italy 23-15 in the opening match.
First-half tries by Alex Cuthbert and Scott Williams gave the hosts a handy 17-3 lead at the break.
Michele Campagnaro, 20, lifted Italy's hopes of snapping a 15-match away losing streak in the championship with two tries to make the deficit five points with 10 minutes remaining.
Leigh Halfpenny's third penalty then gave Wales some breathing space as they made sure there was no repeat of the opening-day defeat by Ireland in 2013.
I thought we were positive in terms of our attacking play but Italy were dogged and competed pretty hard all game.
Wales, looking to become the first team to win three consecutive Six Nations titles outright, will be satisfied with the victory but will want an improved effort in the scrum as they eye tougher challenges in the coming weeks.
"I thought we were positive in terms of our attacking play but Italy were dogged and competed pretty hard all game," Wales coach Warren Gatland told the BBC.
"Defensively I thought our structure was pretty good. Italy made it tough for us.
"I think in the past when we have come under pressure like that we might not have had the composure to finish it off but we did today. We're champions and every team is going to come at us and make it tough."
A long injury list meant Italy coach Jacques Brunel had to name an inexperienced backline, a move that initially backfired as an error by debutant Angelo Esposito allowed Cuthbert a simple try after four minutes.
The Treviso winger failed to gather Rhys Priestland's kick, leaving Cuthbert to collect the ball and collapse gratefully over the line.
After Halfpenny nailed his conversion from the sideline the home team went close to scoring again but Italy's other wing Leonardo Sarto was alert to the danger, booting away George North's well-weighted kick under pressure from four Welsh chasers.
Resolute Italian defence
Italy recovered from the early setback, despite a lack of possession, on the back of resolute defending and the ability to slow the ball down.
The visitors registered their first points through the boot of former Scotland Under-20 player Tommaso Allan after Dan Lydiate was penalised at a ruck.
Italy also troubled Wales in the scrum but a mounting penalty count began to hurt them, allowing Halfpenny to add another three points after captain Sergio Parisse pushed an opponent in a lineout.
The Italians started to test the Welsh defence, Parisse having a try ruled out for a knock-on, but were left to rue their failure to take advantage when Jamie Roberts burst through the defence to send Williams clear.
The visitors got the try their efforts deserved immediately after the restart when Priestland lost the ball in a heavy tackle.
Sarto on the wing kicked ahead and centre Campagnaro put foot to ball again before regathering and diving over the line.
The try was awarded by the television match official despite suggestions of an earlier forward pass.
Neither side was able to take complete control and the match looked to be meandering to its conclusion when Campagnaro doubled his tally with 12 minutes left, intercepting a poor Halfpenny pass to race 60 metres to score.
Wales, boosted by Sam Warburton's return as a replacement after a two-month injury layoff, eased their nerves through the boot of Halfpenny to ensure Gatland's side got their campaign off to a winning, if not completely convincing start.
Dramatic finish in Paris
In the later kick-off substitutes Dimitri Szarzewski and Gael Fickou combined to score a late converted try for France to secure a dramatic 26-24 win against England in Paris.
With two minutes remaining, the hooker Szarzewski made a brilliant break down the left and fed Fickou, and the centrecut inside his marker before running round behind the posts.
England punished weak defending from France to rally from 16-3 down.
No. 8 Billy Vunipola was England's most dangerous player, setting up both tries for fullback Mike Brown and outside centre Luther Burrell on debut as Stuart Lancaster's relatively inexperienced side carved holes in the French midfield in the second half.
Right winger Yoann Huget scored two tries for France in the first half.
Ireland comfortably won their opening Six Nations championship match at the Aviva Stadium on Sunday, taking their time to get going before beating Scotland 28-6 as they look to put last year's poor campaign firmly behind them.
The hosts, who endured their worst Six Nations in 14 years last season, made a slow start and led by just two penalties to one approaching halftime before flyhalf Johnny Sexton sparked them into life and Andrew Trimble grabbed the first try of the game.
They lifted the pace in the second half with Jamie Heaslip, who took over as captain after illness ruled Paul O'Connell out of the game before kickoff, crossing shortly after the break and Rob Kearney added a third try 10 minutes from time.
Ireland, who have raised expectations at home after coming close to beating world champions New Zealand in November, take on Six Nations holders Wales in six days time, the same day Scotland host England.