Relegated Saracens beat Harlequins to dent the Premiership top-four ambitions of their London rivals.
Sean Maitland's early score set Sarries on their way, and Maro Itoje and Aled Davies both crossed before half-time.
Two penalties from Owen Farrell stretched Saracens' lead before Paul Lasike powered over for the visitors.
Scott Steele went over and Lasike's second try put Quins seven points behind with five minutes left, but Alex Lewington ended their comeback hopes.
Harlequins are now nine points off fourth-placed Sale in the table, while Saracens are consigned to a place in the Championship next season after being automatically relegated following persistent salary cap breaches.
Quins fight-back comes too late
Saracens went ahead in the third minute when Billy Vunipola peeled off a maul following a five-metre line-out and fed Maitland to touch down in the corner.
It took Quins over half an hour to get on the scoreboard at Allianz Park through Marcus Smith's drop goal, but the hosts quickly regained the initiative.
A strong carry by prop Sam Crean set the platform for Itoje to dab down, and Davies found space at the side of a ruck to make it 22-3 at the break.
England fly-half Farrell, making his 200th appearance for the north London club, increased the gap to 25 points but the introduction of USA international Lasike spurred Harlequins into action.
The centre powered over after an hour and, after Farrell had kicked another penalty, replacement scrum-half Steele stretched out to grab the visitors' second score.
Lasike then found space in midfield and burst through two attempted tackles to cross the whitewash.
All three scores were converted by Smith to make the score 31-24, but Saracens swiftly put the game beyond their south-west London rivals with a fortuitous try.
A kick forward by full-back Elliott Obatoyinbo was touched in flight by a Harlequins hand and the ball dropped at the feet of Itoje for the England lock to set up Lewington for a bonus-point score.
Both sides play again on Wednesday, when Saracens host Gloucester and Quins travel to Worcester Warriors.
Saracens director of rugby Mark McCall told BBC Radio 5 live:
"We played pretty well in the first half and established a good lead but were very sloppy in the last 20 minutes.
"We allowed a good and competitive Quins team right back into it.
"We were maybe a bit fortunate to get the try towards the end, as it was game-on at that point.
"We need to try and figure out how the games are going to go with the referees blowing the way they are and make sure we adapt better than we did at some times today."
Harlequins head of rugby Paul Gustard told BBC Radio London:
"Largely I was pleased with the performance and the effort of the players.
"We defended well and our scrum was dominant but we didn't control the field well in the first 40. The last play of the first half was the big tipping point in the game.
"Saracens have a lot of talented internationals and are well coached, but we scored three open-field tries against them and caused them problems."
Saracens: Obatoyinbo; Lewington, Morris, Barritt (capt), Maitland; Farrell, Davies; Crean, George, Koch, Itoje, Hunter-Hill, Rhodes, Wray, B Vunipola.
Replacements: Woolstencroft, Barrington, Ibuanokpe, Swinson, Reffell, Whiteley, Socino, Manu Vunipola.
Harlequins: Brown; Morris, Marchant, Lang, Earle; Smith, Landajo; Marler, Baldwin, Kerrod, Lewies, Symons, Chisholm, Robshaw (capt), Dombrandt.
Replacements: Gray, Garcia Botta, Collier, Lamb, Evans, Lawday, Steele, Lasike.
Referee: Christophe Ridley