Harlequins survived a huge scare to beat Bath at Twickenham Stoop after the visitors fought back from 37 points down to set up a grandstand finish.

The bonus-point victory lifts Quins back into the Premiership's top four.

Bath's incredible fightback gives them two bonus points that moves them up to second, five points behind leaders Northampton Saints.

Marcus Smith, Louis Lynagh, Alex Dombrandt and Will Evans tries were bookended by an Andre Esterhuizen double for Harlequins.

Will Muir, Alfie Barbeary, Louis Schreuder, Ruaridh McConnochie and Elliott Stooke replied for Bath to set up an unlikely tense finish in a thrilling game.

However, there was a moment of controversy in the midst of the tidal wave of Bath pressure.

Quins replacement Irne Herbst was sent to the sin-bin in the 64th minute but then returned to the pitch after only seven minutes and went on to make a crucial tackle.

"I flagged it with the referee after the game," Bath director of rugby Johann van Graan said.

"There's not a lot that he can do, on the pitch he wasn't even aware of it. We went through our team manager and we made the fourth official aware.

"On a yellow card, you're supposed to be off for 10 minutes, not seven."

Harlequins started the match brilliantly and were ahead within four minutes as Esterhuizen found the gap between the Bath backline to run through and score between the posts on his 30th birthday.

Smith's clever chip-and-chase over the top ended with the England fly-half dotting down between the posts and converting his own try.

Harlequins added a third score through Lynagh after some quick passing out to the wing from Evans and full-back Tyrone Green.

Having performed so poorly last week at Saracens, the home side secured the bonus point through Dombrandt's sixth Premiership try of the season inside 30 minutes, with the back row breaking off the back of the maul to power over the line.

Flanker Evans got in on the act to score his side's fifth try of the game, with Smith converting in the last action of the half which saw Quins go in 33-3 in front.

The home side started the second half as they did the first, with Esterhuizen scoring his second try of the game at the end of a trademark move involving Lynagh and Oscar Beard, but then the wheels well and truly came off in an extraordinary swing in the match.

Bath got their first try on the board after a TMO review showed winger Muir had grounded the ball over the line in the left corner.

Harlequins were reduced to 14 men when Herbst was sent to the sin-bin before Bath replacement Barbeary scored his fourth league try of the season and fellow substitute Schreuder crossed to cut the deficit to 18 points.

Lynagh was then shown a yellow card and Herbst was reintroduced with Bath wing McConnochie cruising through to secure a bonus point for the visitors.

Replacement Stooke added their fifth try to put the visitors within five points of a remarkable victory but Quins were able to turn the ball over, with Smith booting the ball into the crowd of relieved home fans to end the contest.

Harlequins director of rugby Billy Millard told BBC Radio London:

"First and foremost we had a pretty big week together bouncing back from [defeat by Saracens] last week.

"In the first half we played some of our best rugby, in the second half there was some ill-discipline, a couple of yellow cards and a momentum shift and they got on the front foot.

"Fair play to them for staying in the game, we know they're capable of that from the players they've got."

Bath Rugby director of rugby Johann van Graan told BBC Radio Bristol:

"We kept coming after half-time, this team is never beaten until the final whistle goes.

"Credit to Quins, they gave it to us in the first half but we fought back in the second and we came up just short.

[We're] disappointed we've lost but I'll take the two points and move on.

"We're tough to beat, that's our mantra. Taking a step back, we weren't good enough over the 80 minutes."

Harlequins: T Green; Lynagh, Beard, Esterhuizen, Murley; Smith, Care; Baxter, Walker, Lewis; Launchbury, Hammond; Lewis, Evans, Dombrandt

Replacements: Riley, Marler, Collier, Herbst, Trenholm, M Green, Anyanwu, Anderson

Sin-bin: Herbst (64), Lynagh (71)

Bath: Gallagher; McConnochie, Lawrence, Ojomoh, Muir; Russell, Spencer; Obano, Dunn, Du Toit; Du Plessis, Ewels; Hill, Reid, Coetzee

Replacements: Annett, Schoeman, Stuart, Stooke, Bayliss, Schreuder, Bailey, Barbeary

Referee: Anthony Woodthorpe