If Harlequins make it all the way to Twickenham for the Premiership final in June they can look back and pinpoint this last-gasp victory as a key reason why. Down to 14 men after André Esterhuizen’s second red card of the season and trailing by three points in the final minute, up stepped Marcus Smith to clinch an unlikely victory with a dazzling try to tighten their grip on a play-off place. Smith is enjoying a superb season and a first England cap seems inevitable this summer. This was not his most polished performance but the way the 22-year-old fly-half came to the fore in the closing stages was mightily impressive. Harlequins were trailing by 21-18 when they awarded a scrum penalty near the halfway line. Smith could have had a shot at goal for the draw but instead kicked precisely to the corner and demanded the ball from his scrum-half, Danny Care, before dancing his way through the defence and over the try-line. The Harlequins coach, Nick Evans, said: “I’m probably most proud of the kick because with Marcus, if you put six [men] in front of him, with that amount of space, he’s pretty good at beating people most of the time. “But in that type of mental pressure, you have to put it in the corner to give us a chance … for him to really back himself like that, I’m pretty proud of him.” Given Irish also have play-off hopes, it is a hugely significant win for Harlequins in the race for the top four and keeps Smith and co four points behind Exeter in second place. Irish, meanwhile, only have themselves to blame. Tries from their young wingers Ben Loader and Ollie Hassell-Collins had put them ahead after Esterhuizen’s red card but their inability to see out the game ultimately cost them. It was an ill-tempered contest, scrappy at times but absorbing nonetheless. Irish built an early lead with two Paddy Jackson penalties before Mike Brown registered his 99th Harlequins try, taking a short pass from Care and powering over. The announcement of Brown’s departure at the end of the season has not been well handled but there is no doubting his commitment to the cause on his 350th appearance for the club. Harlequins then lost their openside flanker, Will Evans, to a serious-looking injury but a Smith penalty pushed the visitors’ lead out to 10-6. Jackson notched his third penalty but Harlequins struck with their second try on the stroke of half-time – Cadan Murley going over on the left. Irish started the second half brightly but were given a helping hand by Esterhuizen’s needless red card. A scuffle had broken out near the Harlequins try-line involving Matt Symons, Blair Cowan and Matt Rogerson, and in the aftermath Esterhuizen and Curtis Rona squared up to each other – the South African shoving his elbow into his opponent’s face. It is unlikely to have left much of a mark but the referee, Matt Carley, had little option but to send Esterhuizen off and Irish took all of a minute to capitalise – Loader cruising over down the right. Jackson converted to put Irish back in front. Another Smith penalty soon after nosed Harlequins ahead but the fly-half was at fault for Hassell-Collins’s fine try on the hour mark. Smith picked off Nick Phipps’s pass but did not have the legs to make it to the try-line and threw a speculative offload inside. It was seized on by Irish, who burst through the broken field, keeping the ball alive with a series of offloads, Hassell-Collins finishing off a wonderful try. Irish looked anything but convincing as the clock ticked down, however, and might have turned the screw with a kick at goal rather than to the corner. Harlequins, to their credit, stayed in the fight and Smith seized his chance. London Irish’s director of rugby, Declan Kidney, said: “There were just one or two other opportunities that we probably didn’t quite exploit. And Harlequins did what they’re good at, at the end.”