Evans' opposite number, Miah Nikora, replied with a 17th minute penalty for Connacht and another on the stroke of half-time. But two more successful kicks from Evans had 'Quins leading 13-6 at the break.

Connacht had dominated possession and enjoyed the lion's share of territory up to that point, with a number of their attacking moves breaking down at rucks or missing an incisive pass or two.

The 'Quins defence held firm during an early onslaught from Connacht and Guest's score, after a quick counter from Evans, exposed some lacklustre defending from the visitors.

Connacht tightened things up and got to grips with the breakdown as the first half wore on, and a timely tackle from winger Brian Tuohy prevented the concession of a second try.

Eric Elwood's men were still very much in the game at this stage, aided by some big hits from Michael Swift, Mike McCarthy and Johnny O'Connor, who was winning his 100th Connacht cap.

The front row combination of Brett Wilkinson, who showed his pace on an early run, Sean Cronin and Jamie Hagan also deserve a mention for a solid night's work in the scrum.

Hooker Cronin rumbled up close to the try-line as the visitors started the second half on the up. But again, the attack petered out and the attacking threats of Ian Keatley and Fionn Carr never really materialised.

Harlequins' second try came 10 minutes into the second period and just after Frank Murphy had decided to tap a penalty when Connacht might have been better advised to take the points.

Man-of-the-match Guest then seized upon Keatley's loose pass and set off on a long range run. He fed Mike Brown on his right and the full-back managed to crash over, despite a last-ditch tackle from Carr.

Evans' conversion was cancelled out by Nikora's third successful penalty, in the 57th minute, and although 'Quins had winger Gonzalo Camacho sin-binned for a ruck offence, Connacht could not eat into their lead.

Elwood's charges will be hoping to gain revenge on the Londoners in the return leg next Friday, with 'Quins and leaders Bayonne now five points ahead of them in the Pool 1 table.