Sam Burgess made a 17-minute cameo from the bench as Bath went top of the Aviva Premiership with a 25-6 victory over Harlequins at the Recreation Ground.
England coach Stuart Lancaster will have been delighted to see the rugby league icon's much-anticipated union entrance come at inside-centre.
Bath's head coach Mike Ford has said previously he sees Burgess as a back-row forward but Lancaster believes the 25-year-old can make an impact at next year's World Cup in the centre.
League convert Burgess' last taste of action was on October 5 for the South Sydney Rabbitohs when he played almost the entire NRL Grand Final with a fractured cheekbone.
Burgess had not been expected to make his union debut following his move from Australia for another month - but the Dewsbury-born powerhouse took his place on the Bath bench after Lancaster had described his early return as "a bonus" with the 2015 World Cup in mind.
First-half tries from Matt Banahan and Kyle Eastmond, who had been released from the England squad ahead of Australia's visit to Twickenham on Saturday, helped Bath into a 13-3 interval lead which was not an accurate reflection of their forward dominance.
But Harlequins' fate was sealed in the second half when referee Wayne Barnes produced three yellow cards for the visitors and there was no way 12 men could hold back the Bath tide.
Hooker Ross Batty and number eight Leroy Houston added further tries as Bath secured a bonus-point victory and top spot before the rest of the weekend action.
Fly-half Ollie Devoto made his 50th appearance for Bath but full-back Gavin Henson was a late withdrawal with a sore Achilles.
Harlequins made three changes to the side which lost 16-12 at home to Sale Sharks with scrum-half Danny Care and wing Aseli Tikoirotuma back from respective international duty with England and Fiji.
Blindside flanker Jack Clifford was the only change to the forward pack as the 21-year-old made his first Premiership start and he had his work cut out as Bath opened at a furious pace and were rewarded with an eighth-minute try.
Bath sucked in the Harlequins defence and centres Eastmond and Jonathan Joseph were involved before full-back Horacio Agulla made the decisive break and try-scoring pass to wing Banahan.
With their set-piece dominant, Bath were intent on running the ball at every opportunity and they went through several phases for Devoto to supply the pivotal pass for Eastmond's 18th-minute try.
Devoto was not so precise with his kicking, again failing to add the extras in Henson's absence, but New Zealander Nick Evans was on target to finally get the Harlequins on the scoreboard with a penalty.
But Bath restored their 10-point advantage when the sorry Harlequins scrum was penalised and Devoto landed his first successful kick of the evening from 30 metres.
Bath's pack were celebrating scrums like tries as the 'Quins eight disintegrated time and again but the visitors enjoyed better territory late in the first half and wasted a scoring opportunity when hooker Dave Ward broke the home line.
That revival was reflected on the scoreboard when Evans immediately reduced the deficit at the start of the second half with a penalty - but Harlequins again had to soak up huge pressure close to their line and were relieved to see another Devoto kick sail wide.
But there was no reprieve for tighthead prop Kyle Sinckler, who was yellow carded after yet more 'Quins problems at scrum-time, and the visitors were down to 13 men when lock forward George Robson was sin-binned for collapsing a maul on the try-line.
Referee Wayne Barnes refused to award Bath a penalty try when the scrum went down again but he did reduce Harlequins to 12 men when showing replacement prop Will Collier a yellow card.
Collier's departure led to uncontested scrums and the 63rd minute arrival of Burgess who might have appreciated the reduced numbers from his league days.
The hosts finally made their superior numbers tell when Batty profited from a line-out drive and Houston powered over with seven minutes remaining to take Bath above Northampton Saints and Exeter Chiefs before their weekend games.