|Bath: (13) 25|
|Tries: Banahan, Eastmond, Batty, Houston Cons: Devoto Pens: Devoto|
|Harlequins: (3) 6|
|Pens: Evans 2|
Cross-code signing Sam Burgess came on to make his debut and help Bath overcome a Harlequins side that was briefly down to 12 men.
Burgess, 25, who fractured a cheekbone guiding South Sydney Rabbitohs to their NRL Grand Final win last month, only resumed training recently.
Tries from Matt Banahan and Kyle Eastmond put Bath 13-3 up at half-time.
Quins' hopes faded with three players sin-binned before Ross Batty and Leroy Houston crossed over for Bath.
Nick Evans' second penalty made it 13-6 and Kyle Sinckler, George Robson and Will Collier were then yellow carded.
While the London side resisted the home side's pressure with three men missing, Batty eventually crashed over when Sinckler returned to the action.
The bonus-point try from Houston came against a full complement, completing a dominant performance which lifts Bath to the top of the table overnight.
Victory moves Bath ahead of Northampton and Exeter at the summit, with the Saints taking on bottom side London Welsh on Sunday after the Chiefs face Saracens on Saturday.
Touted as a potential England prospect for next year's World Cup, all the focus ahead of Quins' visit to the Rec was centred on the Dewsbury-born Burgess.
Having agreed to join Bath in February on a three-year deal his arrival was eagerly anticipated even before he produced one of Australian sports' bravest performances by guiding the Rabbitohs to their first premiership win since 1971.
Burgess played the full 80 minutes, despite suffering the facial injury with the first hit-up of the game, to become the first non-Australian to win the Clive Churchill medal for the man of the match.
By the time Burgess took the field for his rugby union debut, replacing Semesa Rokoduguni at inside-centre on 63 minutes, the game had a distinct rugby league feel to it as Bath had space to exploit with Sinckler, Robson and Collier in the sin bin.
Argentine Horacio Agulla, who was a late injury replacement at full-back for Wales international Gavin Henson, made an early impact as he weaved through Harlequins' defence before dishing the ball off for Banahan to score the opening try.
While Ollie Devoto failed to add the extras, he produced a neat flick pass to send Bath's other cross-code convert Eastmond over on 18 minutes.
Devoto then hit the post with his conversion attempt before trading successful penalties with Quins' Evans.
A second three pointer from Evans put the London side back within striking distance of their fellow play-off hopefuls, but poor discipline cost Conor O'Shea's side any real chance of battling back into the contest.
Bath: Agulla; Rokoduguni, Joseph, Eastmond, Banahan; Devoto, Cook; Auterac, Batty, Thomas; Hooper (capt), Day; Garvey, Sisi, Houston.
Replacements: Dunn, James, Palma-Newport, Ewels, Fearns, Stringer, Burgess, Woodburn
Harlequins: Chisholm; Walker, Hopper, Casson, Tikoirotuma; Evans, Care; Lambert, Ward, Sinckler; Matthews, Robson; Clifford, Wallace, Easter (capt).
Replacements: Buchanan, Marfo, Collier, Twomey, Trayfoot, Dickson, Swiel, Turner-Hall.
Referee: Wayne Barnes (RFU)