The Exiles crashed into an early lead through Agustin Creevy, but Josh McNally and a Will Stuart double gave Stuart Hooper’s side a deserved half-time advantage.
Points were sparse for much of the second period until Zach Mercer barged home for Bath’s fourth of the night to seal the result and progression to the last four.
Having faced Irish a fortnight ago, Bath knew to expect a ferocious start from the visitors, and they got just that. Capitalising on home penalties, hooker Creevy peeled away from a close-range maul to reach the whitewash.
Captain Charlie Ewels said Bath let one go at the Brentford Community Stadium two weeks ago, but they were relentless in pursuing their semi-final goal from the sixth minute.
It took just two minutes for the hosts to level. The forwards used the maul, a weapon that has worked well over the past month, to significant effect, driving at a canter, and McNally stooped low to add his name to the scoresheet.
The pack continued to dominate up front; however, Irish remained dangerous on the counter, Creevy and Ben Loader making in-roads.
The Blue, Black, and White’s pride in the jersey shone through, and from a maul turnover, an incredible field-length try followed. Man of the match Mercer picked superbly from the base of the scrum and carried 30 metres before offloading out the backdoor to Taulupe Faletau.
The Wales Number 8 then produced a majestic piece of skill on the run, chipping over the top of the Irish defence and galloping on to cause havoc in their ranks. Joe Cokanasiga slid in to regain possession, wide the ball went, and following a few physical phases, England prop Stuart muscled over for his first.
Jack Walker and Mercer carried hard after that to continue Bath’s onslaught in attack. Beno Obano and Cokanasiga showcased their offloading ability en route to Faletau, charging upfield to the five, a move which Stuart benefitted from once more.
As formidable as they were in attack, Bath were equally as brutal in defence when they needed to be with black shirts swarming round those in white.
Paddy Jackson kicked a penalty on the stroke of the interval to tighten the scoreline to six points ahead of Josh Bayliss and Cam Redpath, proving strong on the gainline early in the second half.
Stuart almost had a hat-trick just short of the hour but was held up, and Ben Spencer charged down a Nick Phipps pass with his boot to send the away outfit into chaos on their own goal-line – Loader hurriedly clearing under pressure.
Jackson nudged his second penalty of the contest in a spell of the game where both teams were evenly matched until Anthony Watson’s brilliant awareness saw him clip the ball into the corner to turn Irish heads.
Bath forced a knock-on from the line-out through their line-speed, and it was rewarded when Mercer finished to round off an impressive night under the Rec lights.
15. Anthony Watson, 14. Joe Cokanasiga, 13. Jonathan Joseph, 12. Cameron Redpath, 11. Ruaridh McConnochie, 10. Orlando Bailey, 9. Ben Spencer; 1. Beno Obano, 2. Jack Walker, 3. Will Stuart, 4. Josh McNally, 5. Charlie Ewels ©, 6. Taulupe Faletau, 7. Josh Bayliss, 8. Zach Mercer
Replacements: 16. Jacques du Toit, 17. Juan Schoeman, 18. Henry Thomas, 19. Mike Williams, 20. Miles Reid, 21. Will Chudley, 22. Max Clark, 23. Alex Gray
15. Tom Parton, 14. Ben Loader, 13. Theo Brophy Clews, 12. Terrence Hepetema, 11. Ollie Hassell-Collins, 10. Paddy Jackson, 9. Nick Phipps; 1. Facundo Gigena, 2. Agustin Creevy, 3. Lovejoy Chawatama, 4. George Nott, 5. Rob Simmons, 6. Matt Rogerson ©, 7. Blair Cowan, 8. Albert Tuisue.
Replacements: 16. Matt Cornish, 17. Harry Elrington, 18. Ollie Hoskins, 19. Chunya Munga, 20. Ben Donnell, 21. Sean O’Brien, 22. Ben Meehan, 23. James Stokes