An injury-time try from England winger Chris Ashton handed Saracens a 42-20 bonus-point win over London Irish at Twickenham.
Ashton's outstretched arm did just enough to scrape the line and hand Saracens maximum points from their opening game of the season.
Never truly threatened for the lead, the title contenders' four tries included a brace from hooker Jamie George.
Irish have been tipped by many for relegation but produced a spirited if ultimately fruitless performance, England winger Marland Yarde one of their two try scorers as they paid the price for frequent penalty offences at the breakdown and scrum.
England fly-half Owen Farrell's penalty opened the scoring and the first try for Saracens shortly followed, hooker Jamie George ducking under the defence to put the 2011 champions 10-0 up after ten minutes.
Irish found themselves on the wrong of a 40-3 drubbing in same fixture at the beginning of last season and they equalled last year's points total with a penalty from Ian Humphreys, the former Ulster stand-off taking on the kicking duties in the absence of the injured Tom Homer.
Saracens defence was a feature of their success last season as they reached the last four of the both the Premiership and Heineken Cup, and it served them well throughout the opening quarter. Irish enjoyed plenty of possession, with David Paice and Jon Fisher carrying well, but had little to show for it.
Handling errors undid much of Saracens good work in attack though and their scrum initially struggled, Irish adapting better to the new engagement laws early on. A second Farrell penalty stretched the lead to 13-3.
Chris Ashton was held up short of the line thanks to some desperate defence from Bryn Evans, but a miscued lineout from Saracens then worked remarkably well in their favour.
Despite losing the ball off the top, Irish's pack were sucked in to where they thought the ball had gone by driving into the maul, only for George to scamper round the back for his second try.
Irish hit back through a try from Kieran Low, the blindside flanker cantering through the Saracens defence after a fine offload from Paice.
Farrell's third penalty though, after Irish were penalised for holding on, extended the lead to 21-10 at the break.
Continued indiscipline from the Exiles after the break cost them dearly - Halani Aulika losing out in his scrummaging battle with Rhys Gill, as Farrell added two more penalties.
In a battle between Saracens' aggression against Irish's endeavour, there was only one winner as continually Irish's best efforts were snuffed out at the breakdown and in the tackle.
Mako Vunipola marked his return to club rugby with a try after returning from Australia with the British and Irish Lions, but his fellow tourist Matt Stevens was sent to the bin for taking out Humphreys off the ball.
Saracens impressive margin on the scoreboard didn't yet include a bonus-point try and instead Irish grabbed a second, the best score of the match created by an offload from Chris Hala'ufia as England winger Marland Yarde raced over untouched.
A sixth penalty from Farrell maintained Saracens' healthy advantage before Ashton finally struck to seal five league points.
For London Irish:
Tries: Low, Yarde
Cons: Humphreys 2
Pens: Humphreys 2
Tries: George 2, M.Vunipola, Ashton
Cons: Farrell 2
Pens: Farrell 6
Yellow Card: Stevens
London Irish: 15 Topsy Ojo, 14 Marland Yarde, 13 Guy Armitage, 12 Eamonn Sheridan, 11 Sailosi Tagicakibau, 10 Ian Humphreys, 9 TomÃ¡s O'Leary, (captain), 8 Jon Fisher 7 Ofisa Treviranus, 6 Kieran Low, 5 Bryn Evans, 4 Nic Rouse, 3 Halani Aulika, 2 David Paice, 1 Matt Parr.
Replacements: 16 Jimmy Stevens, 17 John Yapp, 18 Leo Halavatau, 19 Declan Danaher, 20 Chris Hala'ufia, 21 Andrew Fenby, 22 Shane Geraghty, 23 Darren Allinson.
Saracens: 15 Chris Wyles, 14 Chris Ashton, 13 Joel Tomkins, 12 Brad Barritt, 11 David Strettle, 10 Owen Farrell, 9 Richard Wigglesworth, 8 Ernst Joubert, 7 Jacques Burger, 6 Billy Vunipola, 5 Alistair Hargreaves, 4 Steve Borthwick (c) 3 Matt Stevens, 2 Jamie George, 1 Rhys Gill.
Replacements: 16 Scott Spurling, 17 Mako Vunipola, 18 Petrus du Plessis, 19 George Kruis, 20 Jackson Wray, 21 Ben Spencer, 22 Nils Mordt, 23 Ben Ransom.
Referee: Greg Garner