Ireland hold off Scotland in Dublin
Scotland prop Ryan Grant's World Cup appears under threat due to an ankle injury suffered in 28-22 defeat in Ireland.
The 29-year-old spent the first half of Saturday's Aviva Stadium clash creaking under Ireland's superior scrum pressure, then damaged his right ankle just minutes after the restart.
The Glasgow star could now at best face a race against time to be fit for next month's World Cup, or be ruled out altogether in the coming days.
Blair Cowan, Henry Pyrgos and Peter Horne claimed tries for the visitors, with five of the seven scores in the match after the break.
Veteran centre Gordon D'Arcy's quiet match at the heart of Ireland's midfield could leave the 35-year-old now slipping behind in the race for final World Cup selection.
Prop Dave Kilcoyne and lock Dan Tuohy's odds of making Ireland's 31-man squad may also have lengthened, while flanker Chris Henry has probably now done enough to nail down his berth.
Only Ireland's determination to experiment allowed for Scotland to share the spoils 7-7 at the break, the hosts eschewing four eminently kickable penalties.
Ireland scored from one such foray, flanker Henry eventually burrowing home after unremitting phase play on Scotland's whitewash.
The hosts spurned three similar platforms, however, when in a Test of more importance those penalties would have been aimed at goal.
Cowan popped over in Scotland's sole attack late in the half, the Kiwi-born flanker owing his score to David Denton barrelling over Mike Ross and Ruaridh Jackson delivering a cute pass to Richie Vernon.
Were this the World Cup or even the Six Nations, aside from Ireland's vastly-different starting XV, Joe Schmidt's men would most likely have been 16-0 to the good at the break.
Wholly dominant at the scrum, Ireland bossed the breakdown too, winning a glut of penalties on the ground.
Mike Ross had Grant in his pocket before the Scottish prop's injury, with referee Pascal Gauzere warning the visiting loosehead to bind square on numerous occasions.
Ireland's profligacy nipped at home backsides after the restart, with Scotland scrum-half Pyrgos sneaking over to swipe a five-point lead.
Prop Grant suffered that ankle problem in the build-up to the score.
Tommy Bowe ripped possession away just when the Scots were marauding again and that finally seemed to raise Ireland from their second-half malaise.
Madigan punted another penalty to the corner and from a strong lineout drive Cronin popped over to level the scores at 12-12.
Leinster fly-half Madigan slotted the conversion to wrestle back the lead, with regular captain Paul O'Connell clambering off the bench to raise the impetus again.
Horne's first penalty of the day put Scotland back into a 15-14 lead but that only lasted one minute.
Madigan feinted outside, jinked in and sent Zebo on an angled line and over the whitewash, the successful conversion putting Ireland 21-15 to the good.
The lead changed hands again when Horne raced home after a poor clearance kick from Luke Fitzgerald.
Jackson struck for goal with Horne shrugging off a heavy blow on scoring, edging Scotland ahead 22-21.
Ireland refused to buckle, however, Madigan dabbing an inch-perfect crossfield kick into Fitzgerald's onrushing grasp and the Leinster wing nipped home for the hosts' fourth score.
Madigan's conversion set Ireland up 28-22 with 10 minutes to play and though the playmaker failed with a penalty attempt, the hosts held out for victory.