Ulster now have date with Euro destiny after Saracens defeat
Saracens 33 - Ulster 17
Ulster's route to the Champions Cup quarter-finals has become more complex after they failed to take a single point against Saracens for the second time this season.
Having been comprehensively beaten in Belfast by former Ulster coach Mark McCall's men a little under two months ago, it was a similar story in London.
Ulster had led for much of the first-half thanks to a try by Luke Marshall but failed to add to their advantage.
Michael Rhodes snaffled two of Rory Best's line-out throws, and having been offered the reprieve, the hosts responded mercilessly through a mauled Billy Vunipola try to take the advantage.
Hopes of at least what would have been a priceless losing bonus point flickered briefly when Paddy Jackson reduced the arrears early in the second-half with a penalty but scores from Duncan Taylor, Maro Itoje and Schalk Brits snuffed that out.
For Les Kiss' men, it all meant another day to forget against the Premiership champions - now four defeats in the past three seasons - and their European hopes rest on beating Oyonnax with a bonus point next Saturday and hoping for help from elsewhere to secure one of three best runners-up spots.
An Owen Farrell penalty had given the hosts a lead after just three minutes but a break from Stuart McCloskey set up Ulster for their only points of the half.
He seared past the defensive line before Ulster took turns to barge forward.
Saracens knocked on in their attempt to halt the pack but, advantage in hand, the returning Jared Payne produced a grubber for Marshall to score his third European try of the season.
Jackson converted and a scrum penalty offered Sarries a reprieve but Farrell was off target. As the game entered its second quarter, he did provide three points but, with a chance to take the lead after McCloskey was pinged for holding on, the No.10 again did not connect.
A Saracens error under a high ball gifted Ulster possession deep in the opposition half but their failure to score was telling.
Ruan Pienaar tried a snapped drop goal that arrowed wide of the posts but Ulster signalled for the corner.
When Rhodes rose above the Ulster jumpers, a crucial score before the half became considerably less likely.
Ulster still had possession after Saracens cleared to the sideline but when Rhodes again pinched Best's dart from touch, the opportunity was lost.
As the half-time interval loomed, momentum swung.
Jackson missed a kickable penalty after Andrew Trimble and Sean Reidy had combined to force Richard Wigglesworth into transgressing and Trimble's kick bounced dead moments later with Wiehahn Herbst penalised at the resulting scrum.
It was the prop's final action as he departed with a nasty looking foot injury.
Saracens quickly went for the corner and the younger Vunipola was driven across before Farrell converted.
The half-time scoreline of 13-7 would have been an acceptable outcome for Ulster and Jackson's early penalty in the second-half made matters look all the more promising.
Saracens' response was clinical. First substitute tight-head Ricky Lutton was caught playing the ball on the ground to allow another Farrell three-pointer before a trio of tries in 10 minutes.
Sarries were racking up the phases and when the ball went loose, Ulster sensed the opportunity for a crucial turnover. As George Kruis scooped the loose ball in the direction of Chris Ashton, however, the loss of shape was pivotal.
The recalled England wing broke before releasing Farrell and he accelerated into space. With Payne outnumbered in the corner, Taylor's try was inevitable.
On the hour mark, Itoje was rewarded after Brits had gone within a matter of inches and, as Craig Gilroy went to the sin-bin, the hooker scored after breaking off a maul and exploiting a size mismatch with Ian Humphreys.
The out-half made a more positive contribution for the game's last points when he intercepted the pass of Neil de Kock and scampered home.
By this stage, however, Saracens were already thinking of the knockouts while Ulster contemplated just what they need to join them.
SARACENS: B Ransom; C Ashton, M Bosch, D Talyor, C Wyles; O Farrell, R Wigglesworth; M Vunipola, J George, P du Plessis; M Itoje, G Kruis; M Rhodes, W Fraser, B Vunipola.
Replacements: S Brits (for George, 56), R Barrington (for M Vunipola, 66), J Figallo (for du Plessis, 56), J Hamilton, J Wray (for Fraser, 63), N de Kock (for Wigglesworth, 63), C Hodgson (for Ransom, 63), N Tompkins (for Bosch, 70)
ULSTER: J Payne; A Trimble, L Marshall, S McCloskey, C Gilroy; P Jackson, R Pienaar; K McCall, R Best (c), W Herbst; A O'Connor, F van der Merwe; R Diack, S Reidy, R Wilson
Replacements: R Herring (for Best, 61), C Black (for McCall, 74), R Lutton (for Herbst, 35), L Stevenson (for O'Connor, 74) C Ross (for van der Merwe, 68), P Marshall (for Pienaar, 74) I Humphreys (for Jackson, 63), R Scholes (for Payne, 70)
Man of the match: Owen Farrell