Bath had not won in the league since they edged past Irish 13-12 on October 29, and a fifth successive reversal would have signalled their worst Premiership results sequence for 10 years.
But an early try by prop Anthony Perenise set the tone for an impressive heavy-duty performance from the Bath pack that saw Irish outmuscled.
Fly-half Stephen Donald added a conversion and two penalties to put daylight between the teams, before scrum-half Michael Claassens sealed victory when he rounded off a brilliant 80-metre counter-attack sparked by full-back Nick Abendanon and wing Tom Biggs, then Bath were awarded a penalty try four minutes from time.
Donald finished with 15 points courtesy of three penalties and three conversions, while the Exiles managed a solitary Tom Homer penalty in reply as they slipped out of the Premiership's top four.
Irish showed the effects of just a five-day turnaround from their last league game - in contrast, Bath had more than a week - and that difference told during an attritional contest in gloomy conditions that was lit up by Claassens' touchdown.
And to complete a miserable afternoon for the visitors, their England international full-back Delon Armitage, who had an abysmal disciplinary record in 2011, was sin-binned for a late tackle on Claassens.
Bath boss Sir Ian McGeechan made several changes from the team beaten at Northampton on Christmas Eve, including call-ups for Perenise and his fellow prop Nathan Catt, but centres Dan Hipkiss and Olly Barkley were both sidelined by injuries.
Irish's England centre Shontayne Hape, meanwhile, faced his former club, with prop Alex Corbisiero, hooker James Buckland and lock Nick Kennedy comprising three switches in the pack following a narrow win against Exeter last time out.
Heavy rain and a slippery surface made conditions hazardous for both sides, but Bath settled more quickly than their opponents and they claimed a 15th-minute try, albeit in debatable fashion.
The Bath forwards rumbled towards Irish's line, and referee Martin Fox opted for television match official assistance before awarding the score to Perenise, although replays appeared to show hooker Ross Batty knocking on during the final surge.
Donald added the conversion, and Bath were up and running against an Irish outfit that struggled to contain their opponents' pack power.
Bath had no intention of deviating from a route one approach, and it should have yielded two more tries during a four-minute spell midway through the opening period.
The TMO was called into action on both occasions, and each time he rightly ruled against Bath following handling errors at the crucial moments.
Irish were relieved to escape, but they went 10-0 down when Donald kicked a penalty, and although Homer cancelled out that strike, Bath's superior wet-weather game kept them in charge.
A seven-point interval advantage did not do justice to their monopoly of possession and territory, yet Irish trooped off only a converted try adrift and still firmly in contention.
A second Donald penalty extended Bath's advantage after 43 minutes, and their collective sense of determination was underlined when centre Matt Carraro made a crunching tackle on Homer just five metres from the home line.
Catt and Perenise continued to make life horribly uncomfortable for Irish in the scrums, and Irish were then strung by a memorable Bath try created through Abendanon's daring approach.
He gathered the ball just inside his own 22, then set off on an arcing run, before finding Biggs in support, who found Claassens on his shoulder to complete a stunning breakaway.
Donald converted from the touchline, and Abendanon was at it again just two minutes later, this time going it alone from deep before he was thwarted by some desperate last-ditch tackling.
Another Donald penalty took Bath 20 points clear, then the final ignominy for Irish came when the home side gained a penalty try that condemned them to a resounding defeat.
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