The unerring boot of Nick Evans put Bath Rugby to the sword and earned Harlequins just their second Aviva Premiership Rugby win on the road since January.
Quins travelled to the West Country off the back of a 22-19 defeat at Leicester Tigers last time out, seeking to topple Bath at the Rec for the first time since November 2011.
It was Bath who began the stronger and scored the only try of the first half, through Kyle Eastmond, to hold a narrow advantage at the break.
However, last season’s Aviva Premiership Rugby finalists – who had slipped up at Wasps the previous weekend – came undone in the second half.
Danny Care crossed over to put Quins ahead and they never looked back, Evans amassing 28 points in total from the tee while Dave Ward made sure of the result, before Nick Auterac and Semesa Rokoduguni each grabbed late tries for the hosts.
Eastmond thought he had grabbed an early try after pouncing on a loose lineout but referee Matt Carley ruled the ball had been knocked-on by Bath.
Evans then kicked the game’s first points after David Wilson went in at the side but, shortly before the quarter-hour mark, George Ford notched a penalty of his own when Nick Easter was guilty of the same offence.
Evans restored the lead five minutes later from in front of the posts before Bath responded again, strong carrying in the loose from props Max Lahiff and Wilson taking them near the Quins line.
Anthony Watson was next to come close, only to knock-on as he dived for the line, but the home side did eventually grab the first try.
Patience prevailed deep inside the Quins half and Ollie Devoto found Eastmond out wide to cross over after 32 minutes, Ford expertly converting from the right touchline.
Much of that hard work was soon undone, however, as a pair of quickfire penalties within kicking range allowed Evans to restore Harlequins’ advantage.
But the lead changed hands again shortly before the break, Quins off their feet and Ford bisecting the posts for 13-12 at half time, the tie perfectly poised.
The lead lasted just two second-half minutes, another Evans penalty edging the visitors ahead, and Quins soon grabbed their first try when Care scooped up a loose ball and sniped over.
Evans added the extras to make it 22-13 and slotted another penalty between the posts after 50 minutes to extend the lead even further.
Rokoduguni prevented the task from growing even tougher with a try-saving tackle on Mike Brown but Quins had a penalty advantage from the lineout and Evans made it 28-13.
After 16 unanswered second-half points, Ford stopped the rot with a penalty of his own but once again discipline let Bath down again and Evans responded in kind – his eighth penalty of the afternoon, the most ever from a Harlequins player in an Aviva Premiership Rugby match.
Tim Visser thought he had struck the killer blow 15 minutes from time, on his competitive Quins debut, only for the TMO to spot a forward pass in the build-up.
A yellow card for Eastmond made Bath’s task even tougher and Ward effectively completed the job, collecting Visser’s offload to cross over, allowing Evans to convert once more.
There was still time for Bath to battle back; Auterac capitalising from a rumbling maul to score before Rokoduguni darted over, but it was not enough to pinch a losing bonus point.
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