Alex Waller’s second-half sin-binning was to cost Saints dear as they were beaten 27-12 by Saracens at Allianz Park.
Jim Mallinder’s men were 12-9 up when prop Waller got involved in a scuffle with Saracens’ replacement hooker Jamie George.
Referee Greg Garner spent a long time consulting with TMO Trevor Fisher, discussing Waller lifting his opponent above the horizontal and putting his head into George.
The home fans wanted a red, but the result was a yellow card and it was to damage Saints, who were to concede 12 points while they were a man down.
Ironically, George was the man to stick the knife in first as he peeled off after a lineout to score before his team added a second score via a penalty try.
Waller returned in the 65th minute with Saints well and truly on the ropes and Sam Dickinson was soon in the bin, with Alex Lozowski, who was to end the day with 17 points, adding another penalty.
All this came after four Stephen Myler efforts had given Saints a real chance of ruining Saracens’ first league game at Allianz Park since doing the double last season.
But Waller, who had earlier looked like the victim of a bite from former Saints wing Chris Ashton, was to be left with a hollow feeling as his team headed home with nothing.
Saints had travelled to Barnet on the back of a big win at Bristol last weekend, and Mallinder’s men were to get the first points of the game, through Myler’s boot.
Saracens responded quickly with a penalty of their own, kicked by fly-half Lozowski, and he was soon doubling his team’s tally with another effort from the tee.
It had been a scrappy start with no real pattern to the game and Saints responded after Michael Rhodes’ dangerous tackle on Teimana Harrison, with Myler landing his second penalty of the day.
Little ground was being yielded by either side, with Saints trying to use battering rams Louis Picamoles, Courtney Lawes and Kieran Brookes to break down the door.
The men in white couldn’t get through, but they did get another penalty, which Myler kicked superbly against a strong breeze.
Lozowski again responded in kind, slotting a fine penalty of his own from halfway as the nip and tuck nature of the game continued into the break.
With the wind now at his back, Myler lined up another penalty early in the second half, but his ambitious attempt from inside his own half was to have the length, but not the accuracy.
Saints had started the half well, but they were to suffer an injury blow as Harrison, who had won a couple of important turnovers, was forced off with a shoulder problem.
However, Saints pushed on and after Richard Wigglesworth was penalised for reacting to a Waller nudge off the ball, Myler landed a penalty to put his team back in front.
Saracens were getting flustered in a feisty game, with Saints trying to turn the screw.
But it was to be the away team who lost a man as Waller was punished for a scuffle with George.
George had dragged Waller out of a ruck, with the prop lifting his opponent before the pair grappled on the ground, with the TMO feeling Waller moved his head towards George.
And with Waller in the bin, George, who was involved in a flashpoint with Dylan Hartley at Franklin’s Gardens a couple of seasons ago, rubbed salt in the wound peeling away after a lineout to score.
Lozowski saw his conversion rebound off the right post, leaving Saracens, who had celebrated the try with real fervour, with a two-point lead at 14-12.
It was threatening to be a really costly sin-bin period for Saints, and so it proved as Saracens put the squeeze on with a couple of lineout drives and referee Greg Garner awarded a penalty try.
Lozowski landed the conversion and the gap was nine points, with 14 minutes to go.
Saracens were now in total control and as Saints continued to concede penalties, another man was soon heading for the sin bin.
Dickinson was punished for not rolling away and Lozowski kicked the resulting penalty.
Things were to get worse for Saints as Luther Burrell was left in a bad way after a big collision, with the centre forced off after putting his body on the line.
And there were still more points on offer for Saracens via yet another Lozowski penalty.
Mike Haywood looked like he had responded as he dived over in the corner, but the final pass to him, from Ken Pisi, was deemed forward and the try was disallowed.
It was the last meaningful action in the match as Saints were beaten by a Saracens side who secured their third win from as many matches this season.
Saracens: Goode; Ashton, Bosch (Tompkins 73), Barritt (c), Wyles; Lozowski, Wigglesworth; M Vunipola (Barrington 73), Brits (George 50), Du Plessis (Figallo 40); Itoje, Hamilton; Rhodes (Wray 55), Burger, B Vunipola.
Replacements: Barrington, Brown, Spencer, Tompkins, Maitland.
Saints: Tuala (Mallinder 70); K Pisi, G Pisi (Foden 68), Burrell (Ma’afu 74), North; Myler, Dickson (Groom 64); A Waller (Clare 74), Haywood, Brookes (Hill 64); Lawes, Paterson (Dickinson 64); Wood (c), Harrison (Gibson 49), Picamoles.
Replacements: Clare, Ma’afu.
Referee: Greg Garner