Smith shone throughout and marked his 200th Quins appearance with the opening score as Seb Driscoll, a penalty try and Cadan Murley's ninth London derby try secured rock-bottom Quins a bonus point before half-time.

Sarries stayed in touch with tries from Rotimi Segun and Theo Dan before the turnaround, but two yellow cards made their task harder.

The second half was a tighter affair but Quins extended their lead through Will Porter and despite Nick Tompkins' consolation score, the hosts recorded a third straight home Prem win over their rivals, who could have gone second with victory.

Quins stay bottom but are now only one point behind Exeter and Newcastle with Saracens in fifth, five points behind early leaders Gloucester.

England fly-half Smith set the tone inside three minutes, darting through after some quick handling down the left flank and then converted his own try.

Saracens gave up a series of penalties in the opening stages allowing Quins to pile on the pressure and Driscoll burst through Tomos Williams for the second score after 15 minutes following a bulldozing run and quick pass from England prop Fin Baxter, who was making his first start in 10 months.

The visitors pulled one back four minutes later when Segun jinked to the line in the corner after a quick pass from Max Malins but Quins were undeterred and were awarded a penalty try on 24 minutes when a rolling maul from a lineout was dragged down on the line, with Ben Earl being shown a yellow card.

Sarries thought they had closed the gap further when Malins scampered over the line after Segun brilliantly kept the ball in play but Smith stole in from behind to slap the ball away before the unsuspecting Malins could ground it.

Moments after Earl returned to the fray, Fergus Burke was sin-binned for a head-to-head tackle on Quins' Rodrigo Isgro as he surged towards the line and the hosts made them pay within 60 seconds as Murley gathered a long pass on the left flank and dived into the corner for his ninth London derby try.

Saracens did reduce the arrears with the final play of the half with Theo Dan touching down following a rolling maul from his lineout.

Burke was not allowed to return from the bin after failing a head injury assessment [HIA] with Angus Hall coming on in his place with Malins switching to fly-half before Sarries made five changes in the pack just seven minutes after the turnaround.

Porter pounced on a drop from Segun following Williams' long pass to kick ahead and then stiff-arm his way to the line to extend the lead on 55 minutes, with Smith slotting the extras.

Tompkins bounced his way over after a maul on 62 minutes to reduce the arrears but Hall hooked his conversion attempt wide and Sarries were unable to conjure a late bonus point in the face of some solid Quins defence.

Replacements: Staples, Hobson, Delgado, Williams, Browne, Evans, Friday, David.

Replacements: George, O'Driscoll, Clarey, Tizard, Isiekwe, Gonzalez, James, Hall.