Paris - English side Saracens avenged last weekend's defeat to two-time European Cup champions Munster with a solid 19-13 victory in an engrossing contest on Sunday to go top of Pool 1.
Scoring honours, though, went to French side Toulon.
Having made heavy weather of their win against struggling English side Sale in last weekend's fixture they had no such worries back in France, trouncing the same opponents 62-0 to move five points clear in Pool 6.
Their fellow Top 14 side Castres had opened the day's proceedings with a dire display in a 10-8 home win over Scottish outfit Glasgow to move second in Pool 4, three points behind Ulster.
Saracens' victory saw them move onto 14 points, two clear of Racing Metro with Munster, who took a point with a defensive bonus, a further point behind with two games remaining.
"It was a very, very important game and this time round we did the little things really well which was crucial," said Saracens captain Steve Borthwick.
His Munster counterpart Doug Howlett took defeat graciously but said that they were far from out of contention.
"It was a hard fought battle where defence was the dominant factor," said the former All Black, who scored his side's only try.
"There are a lot of what ifs from the game. However, we have lost the battle but not the war."
Richard Wigglesworth created Saracens try, his deft grubber kick into the corner catching the Munster defence flat-footed, which was touched down by England wing David Strettle.
Owen Farrell added the conversion to give the hosts a 10-3 lead 21 minutes into the match.
However, a loose pass by Farrell four minutes later saw centre James Downey intercept just inside Munster's half.
The former Northampton back charged down the pitch but realising he was not going to make the line he offloaded to Howlett who scored his 10th try in the competition. Ronan O'Gara converted for 10-10.
Farrell subsequently missed two relatively simple kicks at goal and O'Gara showed him how to do it with a delightful long range penalty with 30 minutes remaining to give Munster the lead for the first time 13-10.
However, Farrell recovered his composure in the pouring rain to kick two penalties to give the hosts a 16-13 lead.
Saracens, though, were reduced to 14 men in the 62nd minute when French referee Jerome Garces showed a yellow card to flanker Will Fraser for what he adjudged a high tackle on Howlett.
The visitors, though, were unable to take advantage of that with O'Gara missing with a drop goal and then a penalty in the unrelenting rain and with less than five minutes remaining Farrell added another penalty.
Toulon ran rampant against Sale, who have failed to register much of a revival since former All Black coach John Mitchell took over at the end of last month, with nine tries, seven of them in the second-half.
Several of their foreign stars got in on the try feast, former Springbok Joe van Niekerk scoring two while the Armitage brothers Steffon and Delon also scored a try apiece.
France flyhalf Frederic Michalak contributed 20 points, including a try.
Castres only secured their win - their 14th successive home victory - when the visitors were reduced to 13 men with 10 minutes remaining and they scored their only try of the game through Yannick Caballero.
Glasgow, who along with Edinburgh have yet to secure a win for the Scottish sides in their eight games this season, had a chance to win it but Scotland fly-half Ruaridh Jackson's penalty hit the post.
Results from the fourth round of pool matches in the European Cup on Sunday:
Saracens (ENG) 19 Munster (IRL) 13
Castres (FRA) 10 Glasgow (SCO) 8
Toulon (FRA) 62 Sale (ENG) 0
Played on Saturday:
Ospreys (WAL) 17 Toulouse (FRA) 6
Treviso (ITA) 13 Leicester (ENG) 14
Harlequins (ENG) 53 Zebre (ITA) 5
Ulster (IRL) 9 Northampton (ENG) 10
Exeter (ENG) 30 Scarlets (WAL) 20
Leinster (IRL) 21 Clermont (FRA) 28
Montpellier (FRA) 34 Cardiff Blues (WAL) 21
Played on Friday:
Edinburgh (SCO) 3 Racing Metro (FRA) 15
Biarritz (FRA) 17 Connacht (IRL) 0