Saracens edged closer to the European Cup quarter-finals on Friday with a gritty 16-13 victory over Ospreys which ended the Welsh side's six-year, 17-match unbeaten home record in the tournament.
The win gave the English champions 14 points at the top of Pool Five, two ahead of Biarritz who picked up a bonus-point 29-12 victory over Treviso, while defeat virtually ended Ospreys hopes of making the last eight.
In the night's other match, Edinburgh defeated Cardiff Blues 19-12 in Pool Two. Both sides are locked at the top on 13 points after the Welsh outfit collected a losing bonus point.
In a bad-tempered clash at Swansea's Liberty Stadium, Saracens centre Owen Farrell and Ospreys fly-half Dan Biggar exchanged two penalties apiece for 6-6 after 26 minutes.
But a minute later, the English Premiership champions, who won the first match between the two sides 31-16 at Wembley last weekend, grabbed the only try of the first half.
An attempted clearance by Biggar was charged down by fly-half Charlie Hodgson before No.8 Ernst Joubert, who scored at Wembley, was fastest to the loose ball to touch down.
Farrell added the extras for a 13-6 lead which became 16-6 at the interval with another Farrell penalty awarded just after Ospreys prop Paul James had been yellow-carded.
Biggar missed a penalty early in the second half before centre Ashley Beck, who scored twice at Wembley, had a try ruled out by the video referee when he fell short of the line.
Saracens were reduced to 14 men when South African hooker Schalk Brits was red-carded.
Moments after his return, lock forward Kelly Brown was also sin-binned for tripping Biggar.
Ospreys, who were comfortably on top at that stage, made the one-man advantage count with veteran lock Ian Gough going over in the corner off a sweeping pass from Biggar in the 65th minute.
The fly-half nailed the conversion to cut Saracens' lead to 16-13, but solid and tight defence saw the English side home.
In France, Biarritz came from 12-3 down against Treviso to run in four tries and clinch a 29-12 win. Dane Haylett-Petty, Arnaud Heguy, Wenceslas Lauret and Iain Balshaw all scored tries.
However, Biarritz's win was overshadowed by No.8 Imanol Harinordoquy being forced off the field after just 22 minutes with a left knee injury.
Edinburgh avenged last week's 25-8 loss to Cardiff with a 19-12 which ended the Welsh side's perfect start to the competition.
Cardiff opted against handing a debut to centre Gavin Henson, but five of the team's World Cup players did start the game.