La Rochelle threw Pool Five wide open as they became the first side in 18 games to win at Gloucester.
In a match marred by indiscipline, the French visitors prevailed 24-18.
Smarting from their 13-6 home defeat to the Cherry and Whites last weekend, La Rochelle shocked their Premiership opponents, for whom even two tries from Lesley Vainikolo could not save the day.
A fiery second half saw the visitors lose both Alexandre Bares and Tamato Leupolu to the sin bin, while Vincent Roux was sent off for picking up two yellow cards.
The home side dominated territory but did not convert their chances and once number eight Thomas Soucaze powered his way over, they were chasing the game.
Benjamin Dambielle collected a 14-point haul and prop Jonathan Garcia also touched down for La Rochelle.
Vainikolo crashed over either side of the break and Freddie Burns crossed for a late try in a frantic final 10 minutes but it came too late.
Leeds completed a double over Crociati in the Amlin Challenge Cup while a win for Newcastle denied Exeter the lead in Pool Three.
Leeds Carnegie completed a double over Crociati in the Amlin Challenge Cup as they won 44-6 on the road to make it 99 points in the back-to-back games against the Italian side in Pool 4.
It was nip and tuck in the first half as the home side hit back after falling 12 points in arrears to reach half-time only 15-6 behind.
But there were five second-half tries from the visitors to keep them in touch with pool leaders Stade Francais.
The unbeaten Frenchmen beat Bucharest Oaks 35-7 to move to 19 points after four rounds.
Leeds are five points behind and have to travel to Paris in round five in the new year.
The Aviva Premiership side got off to the perfect start with a penalty try after only five minutes and then added another 20 minutes later from Mike Stevenson.
Ceiron Thomas converted one and then added a penalty before the break after Tommaso Iannone had clawed back six points with two penalties.
But it was one-way traffic after the break with the bonus point coming on the hour after further tries from Phil Nilsen and Welsh international Rhys Oakley.
A last-quarter flourish saw Luther Burrell cross and then Henry Fa'afili crash over for a pair of tries.
Newcastle Falcons had to transfer their Pool 3 game with Exeter Chiefs to Galashiels after their snow-covered Kingston Park ground was ruled out, and an 80th-minute penalty from Jeremy Manning earned them a 26-24 victory just as it seemed they were set to lose.
Having transferred their visitors safely over the border, they then went on to rock their hopes of reaching the quarter-finals by beating them for the first time in three meetings this season.
The reliable boot of Jimmy Gopperth gave the Falcons a flying start as he kicked four penalties to add to a try from South African Gcobani Bobo as Newcastle reached the break 17-6 ahead.
A fifth Gopperth success made it 20-6 shortly after the re-start, but the Chiefs came thundering back into the contest with tries from centre Phil Dollman and wing Mark Foster.
Ryan Davis weighed in with 12 points and when Gareth Steenson converted Foster's 76th-minute score the Chiefs took the lead for the first time.
But then Manning stepped up to steal the glory and rob the Chiefs of the chance of taking over at the top of the pool from Montpellier, who were beaten 36-18 in Bourgoin.