The boot of Barry Everitt kept London Irish in the top three of the Zurich Premiership and left Bath, the one-time giants of the English club game, in desperate straits and facing the real possibility of relegation.
Bath's experiment of playing England's Iain Balshaw, a back-three specialist, did not really pay off, despite his landing two enormous drop goals in the first half, and although he was quick, and showed a willingness to run the ball or ship it, he still lacked experience against such a streetwise side as Irish.
Once they got under way, the well-organised Exiles had too much pace out wide and too much steel in midfield. They defended superbly and confidently outmuscled Bath at the breakdown – one immense shove, deep into the second half, saw them drive Bath off the Exiles' line and back almost to the M4 motorway.
For their part the West Country side, who did put up some fight but far too late into the match, fell foul of Bristol referee Steve Leyshon too often for their own good and Everitt rarely misses his kicks at goal, as his eight penalties and one conversion illustrated.
Both sides had set off at a blistering pace, Bath ever prepared to run the ball from deep and Irish just as ready for hand-to-hand combat themselves. The difference was that the Exiles appeared to have a little more power and motivation, especially early on.
Despite all the hands-on stuff it was good footwork which got the scoreboard ticking over. Bath's Ollie Barkley staggered Irish fans with a 50-metre penalty, while Everitt's second success was cancelled out by Balshaw's first drop goal.
But the relentless pace continued. Paul Sackey, the London Irish right wing, had already made a couple of probing runs, only a Rob Thirlby tackle keeping him out in the 10th minute. But Sackey caught Bath napping in the 29th minute when his 15-yard dash was followed by a wicked cross-chip that the full-back Michael Horak pounced upon for the opening try.
Thereafter Irish piled on the pressure. Balshaw's incredible boot served up another gargantuan kick over the uprights but Everitt extended the home side's lead with his third penalty.
By then Bath had already hauled off their lock Mark Gabey and replaced him with the England second-row Steve Borthwick. Not that he was able to stem the tide. The Exiles had a taste for the action and continued to make life miserable for the visitors, who emerged after the interval without their captain and No 8, Dan Lyle.
Bath and Barkley plugged away but as often as they made ground, there was their nemesis, Everitt, thumping them back where they came from with huge kicks from hand.
London Irish: M Horak (J Brown, 80); P Sackey, G Appleyard, B Venter, J Bishop; B Everitt, H Martens (D Edwards, 49); M Worsley (N Hatley, 61), N Drotske (R Kirke, 46), R Hardwick (S Halford, 46), R Strudwick (capt), S Williams, P Gustard (E Halvey, 61), C Sheasby, D Danaher.
Bath: R Thirlby; T Voyce, M Tindall, O Barkley, S Danielli; I Balshaw, K Dalzell (G Cooper, 50); S Emms, A Long (M Regan, 53), J Mallett (D Barnes, 48), M Gabey (S Borthwick, 33), D Grewcock, G Thomas, D Lyle (capt; N Thomas, h-t), J Scaysbrook.
Referee: S Leyshon.Reuse content