The in-form winger followed up his double at Leicester last week by running in Sarries' fourth try as they took themselves four points clear of Harlequins at the summit.
It rounded off a difficult week for Welsh, who find out their fate over the alleged ineligibility of scrum-half Tyson Keats at an RFU hearing on Tuesday which is threatening to seal their fate in their battle against the drop.
The visitors got off to a disastrous start when Keats' kick in the first minute was charged down by Alistair Hargreaves, leading to a penalty and an easy three points for Charlie Hodgson. Saracens soon doubled their lead when Hodgson was given another simple kick at goal from under the posts.
A horribly-executed scrum then led a Welsh player being penalised for going in off his feet at a ruck, but Hodgson this time kicked wide. Completely against the run of play, London Welsh scored the game's first try after 26 minutes when Julio Cabello's off-load bounced nicely for Seb Stegmann on the left wing.
The debutant sold two Saracens players a dummy and sauntered over, although Gavin Henson missed his conversion. But the visitors then lost Canadian winger Phil Mackenzie to the sin-bin and a few minutes later conceded a penalty try as a Sarries lineout led to a maul that was illegally dragged down.
Prop Tom Bristow was yellow-carded for the offence, but while they were down to 13 men, Henson knocked over a penalty. Yet more ill-discipline from the Exiles allowed Hodgson to slot another penalty before Henson reduced the gap to 16-11 with a scrappy drop goal that clipped the crossbar right on half-time.
Saracens managed to put more daylight between the sides seven minutes into the second half when Joel Tomkins held off his tackler to score, with Hodgson converting. To London Welsh's credit, they cut the deficit down to nine points with another Henson penalty.
But Sarries took a huge step towards victory just after the hour mark when Strettle found Schalk Brits, whose off-load allowed Will Fraser to just about finish in the corner, with the try awarded by the TMO.
The visitors thought they had a route back in the game when Henson touched down on the right wing - only to see the try chalked off for obstruction by Tom Arscott in the build-up. And Saracens sealed the bonus point with eight minutes remaining after Strettle went through a gap that appeared to be made by Tomkins holding back Henson.