The classy Australian full-back scored two tries and created another as Super League leaders St Helens bounced back from last week’s loss against defending champions Leeds Rhinos.
But Rovers – who trailed just 14-6 at the break – will be kicking themselves for failing to do more on a disappointing night at KCOM Craven Park.
More worryingly, they lost George Lawler to a badly broken leg and dislocated ankle while Danny McGuire and Andrew Heffernan also departed with concussions that will see them all miss the Good Friday derby with Hull FC but the luckless Lawler much longer.
Tim Sheens’s side enjoyed much of the play but were largely unable to capitalise, mainly down to numerous ill-conceived last-plays.
Time after time they tried running on the last tackle – not all were pre-planned – and each time, one way or another, it ended in disappointment.
When they did opt for the kick, more often than not McGuire and Chris Atkin caused Saints problems.
However, too often, the league leaders were let off the hook and, in the second period, Rovers’ discipline fell away while, criminally, they not only sailed the game’s kick-off dead via Ryan Shaw but also saw Adam Quinlan repeat the error in the second period.
They had hoped to build on last week’s impressive win at Huddersfield – only a second since promotion – but now there will be added pressure as they prepare for that Craven Park meeting with FC, their first derby in almost two years.
“We have a couple of serious ones (injuries),” said Sheens afterwards.
“George broke the leg and dislocated the ankle, it could be a compound break. It couldn’t be any worse to be quite honest.
“It’s one of those real ugly ones. We won’t see him for quite a while. Hopefully, he’ll be back this season but the damage around the ankle is always the worry. I’ve seen it finish players if the cartilage is damaged badly.
“Danny McGuire’s off to hospital too with a bad concussion he got at the end and he could be out for a while.
“Heffernan is concussed as well and none will play next week.
“We had 12 on the field when they scored twice at the end. We couldn’t do anything about it as the 13th man wasn’t allowed back on either with his HIA as well.
“We’ve probably had four head knocks tonight so it was a very tough night at the office.
“We’re disappointed as the effort was there but we just didn’t execute.”
In fairness, Rovers would always be up against it last night after losing two players in the first half.
Lawler, playing only his third game since a major pelvis injury, was stretchered off with that painful injury - the hooker needed gas and air on the pitch - in the 17th minute and, later, in-form centre Heffernan departed concussed.
But Shaw gave them plenty of hope with his fifth try of the campaign, a lovely effort in the last play of the half.
It was the least Rovers deserved and it came following some terrific handling, not least from second-row Chris Clarkson and also Thomas Minns as the right winger was eventually ushered over in tight conditions.
The hosts would have been irritated if they had not scored as they had enjoyed much of the play only to be hamstrung by those shoddy final options.
For Saints, Luke Thompson went route one to score in the 15th minute, the in-form prop barging through from 15m out and then stretching over on his 100th Super League appearance.
Danny Richardson converted and added a penalty before his side capitalised on a rare Rovers error in their own half when Ben Kavanagh spilled Robbie Mulhern’s pass and, from the scrum 40m out, Barba struck for his seventh try of the season.
He has been in devastating form so far and showed his electric pace here although, in reality, it was one of his easiest scores; Heffernan slipped first and then so did McGuire for a gaping hole to appear.
Heffernan’s night come to an early end when he painfully got his head in the wrong position trying to defend a charging Louie McCarthy-Scarsbrook from the restart. That saw replacement back-row James Greenwood act as a makeshift centre but it did not prevent them finally getting that score.
Saints had generally defended Rovers’ shift plays well but Justin Carney at last found some space down the left and, though he was denied, they passed back to the other flank for Shaw to finish with aplomb, also improving himself.
However, his side suffered more of the same in the second period and, still fuming for being penalised for crossing when in attack, they could only watch on as Barba finish his second in the 56th minute.
Tommy Makinson came in off his wing to smash Atkin on another last play gone wrong, summing up KR’s night, and it was left to Barba to finish them off.
His beautiful long pass sent Makinson free down the right and Jonny Lomax arrived to finish in the 69th minute.
When Quinlan erred from the restart, Dom Peyroux slalomed his way through for a soft try to make sure. That said, the full-back did make a stunning try-saving tackle to deny Regan Grace, and Rovers’ effort could not be faulted.
Hull KR: Quinlan; Shaw, Heffernan, Minns, Carney; McGuire, Atkin; Mulhern, Lawler, Masoe, Blair, Clarkson, Kavanagh. Substitutes: Lee, Donaldson, Greenwood, Walne.
St Helens: Barba; Swift, Makinson, Percival, Grace; Lomax, Richardson; Amor, Roby, Thompson, Peyroux, Taia, Wilkin. Substitutes: Fages, McCarthy, Douglas, Knowles.
Referee: Liam Moore (Wigan).