Gloucester began well but, thereafter, the performance seemed flat. In particular, the inability to hold on to the ball beyond one or two phases prevented Nigel Davies' side from getting any real foothold in the game.
After three wins already this season over the same opponent, it was an unexpected setback.
That's not to take anything away from the visitors who are fighting for their lives at the foot of the Aviva Premiership table. They battled well and gratefully accepted anything that went their way.
Especially what proved to be a gift of a try just before half time, when George Skivington scored his second from absolutely nothing after Shane Monahan fumbled inside his own 22.
Gloucester responded with plenty of endeavour, but it wasn't meant to be on the day. The game was still there to be won in the closing stages, but half chances weren't converted and Irish hung on for a vital win.
For Gloucester, it's now about how they respond. Two weeks of Challenge Cup action lie in wait. Gloucester currently head the pool and will be seeking to clinch a quarter final spot.
In terms of the Aviva Premiership, Gloucester's next games are testing trips to Northampton Saints and London Wasps. A lot will be riding on those games.
The afternoon started on a poignant note.
Gloucester Rugby Mike Nicholls sadly passed away over the Christmas period, and a number of his team mates lined up on the field to join the two teams in an impeccably observed minute's silence.
Gloucester started brightly, with some fine interplay between backs and forwards, and a penalty was quickly awarded. From wide on the right, Freddie Burns confidently opened the scoring with a well struck kick.
However, the visitors were quickly back on level terms. Gloucester conceded a penalty at a set scrum head on to the posts, and Steven Shingler had no problem making it 3-3 after 12 minutes.
Billy Twelvetrees nearly engineered an immediate response, as his powerful run took play into the Irish 22 but a knock on near the line allowed Irish to clear.
Shane Monahan got back to gather the kick, but Gloucester offended at the ensuing ruck. However, Shingler's penalty struck the left hand upright and bounced clear.
Gloucester were a bit loose at this stage. Plenty of ambition, but not quite the execution to match. As a result, the visitors were still well and truly in the game.
And it was Irish who struck next and took the lead. A good maul set up promising field position, and smart offloading took play to within a couple of metres of the line. George Skivington promptly stretched over to score and quieten the home crowd. 3-8 after 26 minutes.
Handling errors continued to haunt Gloucester and kill off any attacking momentum. The frustration level was growing, not helped when Burns was short with a long range penalty, and the Cherry and Whites needed a spark.
Burns did reduce the arrears on 35 minutes as Irish were pinged at a set scrum, and then marched back a further ten metres for back chat. The penalty narrowed the gap to 6-8 but the visitors still had the advantage.
Disaster then struck as Monahan completely misfielded an innocuous looking kick into his own 22. The loose ball was gathered by Irish, popped up and Skivington fell over the line for his second. Shingler converted for a 15-6 half time lead.
It had been possibly Gloucester's worst 40 minutes of the season. Aside from the first few minutes it had been a tale of Gloucester errors, and the visitors couldn't really believe their luck at having had to work so little for their scores.
One consolation was that Gloucester couldn't possibly play so badly again in the second half. But it was going to take a big 40 minutes to overhaul a team who now had their tails up.
Gloucester certainly showing plenty of determination after the break, but the early stages were still littered with way too many unforced errors from the home side.
Burns was off target with a 50th minute penalty as the tension grew, and Nigel Davies made a triple change, sending Nick Wood, Matt Cox and Dan Robson into the fray.
A furious spell of pressure followed, but Gloucester couldn't quite press home their advantage despite powerful running from Monahan and Morgan. Irish killed the ball and Burns slotted his third penalty for 9-15 as the hour mark approached.
Burns then added his fourth penalty and it looked to be game on with 18 minutes to go with Gloucester trailing by just three points.
However, the visitors cleverly took time off the clock, spending time in Gloucester territory and were eventually rewarded with a penalty on 72 minutes. Tom Homer stepped up and bisected the posts for 12-18.
Digging deep despite the body blow, Gloucester sought desperately to drag themselves back into contention and there were brief glimpses of hope.
However, the visitors were in no mood to concede a late score and Gloucester were left to reflect on what might have been.
|Gloucester Rugby Score Card|
|London Irish Score Card|