Ireland 24 Japan 14
This Ireland team don't tend to make things easy for themselves but even by their own standards, this was far too close for comfort.
Ultimately, they got the job done against Japan as they avoided one of the biggest upsets in World Cup history but it was a disjointed performance that posed more questions than answers.
Ireland deserve credit for the manner in which they fought back from a 14-0 half time deficit but they never should have found themselves in such a position that threatened to leave their World Cup dream in tatters.
It wasn't until the 73rd minute that Ireland eventually took the lead for the first time as Nora Stapleton held her nerve to slot a late penalty before replacement Paula Fitzpatrick made sure of a precious win with her second try.
Attentions now turn to France on Thursday and on this evidence, major improvements will be needed if the hosts are to have any hope of competing in the semi-final when the tournament moves to Belfast.
Fitzpatrick had a big impact from the bench and it was her try that eventually drew Ireland level but Sene Naoupu's influence was also pivotal.
Defensively Ireland were a mess. Jenny Murphy's absence was felt as the hosts' line speed was non-existent. Naoupu however eventually grabbed the game by the scruff and those around her fed off the powerful centre's intensity, both in defence and attack.
Worryingly, Japan's attack looked far more threatening throughout the first half as they cut their opponents defence to shreds at an alarming rate.
Debutant Nicole Cronin brought plenty of zip to Ireland's play early on but she wasn't helped settle into international rugby by those around here looking increasingly nervous.
Time and time again, Ireland were guilty of forcing the issue and consequently Japan grew in confidence.
Not much was expected of this Japanese team, particularly after they shipped 72 points to France in their opener but their skill set was vastly superior to that of Ireland's.
The sloppy errors were killing any momentum that Tom Tierney's side threatened to build and their discipline soon went out the window as well. They were penalised for three high tackles in what was an appalling first half display.
The warning signs had been glaring before Japan eventually struck for the opening try shortly before the half hour mark.
A huge shove from their front-row deep inside the Ireland 22 won a penalty against the head but worse was soon to follow.
Japan opted for another scrum from the resulting penalty and again they demolished the Irish pack as referee Ian Tempest went under the posts and awarded a penalty try to put the visitors into a 7-0 lead that they full merited.
Tierney responded by bringing first choice tighthead Ailis Egan off the bench but she couldn't stop Japan doubling their advantage before the break.
Again, Ireland struggled to get out of their 22 and Japan made them pay. The TMO had ruled that Iroha Nagata hadn't grounded the ball but it mattered little as a minute later, Japan injected pace and width into their game-plan and when Ali Miller shot up off her line, Mayu Shimizu scored to stun the sold out crowd at the Belfield Bowl into silence.
Shimizu converted for her own try for a 14-0 half time lead to leave Ireland facing an uphill task to keep their World Cup dream alive.
Tierney would have been furious with his side's penalty count but his talk at the break had little effect as Katie Fitzhenry was shown a yellow card three minutes after the restart for a fourth high tackle.
But that sin bin eventually woke Ireland up. Stapleton put in a clever kick over the top but it was matched by Miller's superb chase and she managed to block down to clearance to bring her side deep into Japanese territory.
Tierney had rung the changes and two of his substitutes Leah Lyons and Fitzpatrick had a big impact in hauling them back into the game.
Lyons and Fitzpatrick were both stopped short of the whitewash but there was no stopping Miller who had spotted a narrow gap and squeezed over after 45 minutes.
Stapleton's conversion halved the deficit as Ireland finally gave the home crowd something to shout about.
Nauopu put in a shuddering hit under her own posts after 55 minutes to force a crucial penalty that brought the crowd to their feet.
The majority of the 3,500 at the Bowl were up on their feet again nine minutes later when Ireland drew level.
Louise Galvin forced a penalty inside the Japan half and when Ireland set up a powerful rolling maul for the first time in the game, Japan had no answer to their power.
Fitzpatrick was credited with the try and it was no more than her barnstorming performance from the bench deserved.
Stapleton's conversion was soon followed by a nerveless penalty to put her side in front with seven minutes remaining.
Fitzpatrick crashed over for her second try in stoppage time and player-of-the-match Stapleton's extras put some respectability on the score line.
If Ireland had an extra five minutes to play with, they almost certainly would have secured the bonus point but they would have scarcely deserved it.
As it was, they had to settle for avoiding a huge upset and maintaining their winning start. Ultimately that's all that matters but they know that France will not be as forgiving.
IRELAND – M Coyne (L Galvin h-t); H Tyrrell, K Fitzhenry (J Deacon 52), S Naoupu, A Miller; N Stapleton, N Cronin; L Peat (R O'Reilly h-t), C Moloney (L Lyons h-t), C O'Connor (A Egan 28); C Cooney, S Spence; C Griffin, A Baxter (P Fitzpatrick 43), C Molloy (capt).
JAPAN– M Shimizu; E Hirano, I Nagata, R Kurogi, H Tsutsumi (A Suzuki 76); M Yamamoto, M Tsukui (Y Noda 61); M Ebuchi (M Suzuki 64), S Saito (capt), S Minami (M Kataoka 74); A Mimura (A Nakajima 36), A Sakurai, Y Sue, S Suzuki, M Takano (Y Shiozaki h-t).
REF – I Tempest (England)