Quins had their rugby league players to the fore, Robbie Paul and Gary Connolly made numerous dents in the Scots' line, but Caledonia had their stars too; the full-back Rowen Shepherd provided exciting thrusts upfield and telling incursions into the line and McIvor and his pack battled for everything up front and around the park.
There was no doubting the Scots' commitment from the outset. They may not have won a match but they did not allow Harlequins to pull away during a first half that had its scraps and scrappy moments as well as some gems. Quins' first score was a perfect example. Jamie Williams was allowed to make the finishing touchdown to a wonderful opening movement that swung first one way and then another as the Scots' defence was probed and prodded by the inventive Quins.
There was more to come. The hooker Keith Wood, who has shown himself to be a force in midfield as well as being so able at the set-pieces, picked a stunning line of running that split the Scots' defence and sent Williams away. He gave a scoring pass to Jim Staples for the first of the Irish full-back's hat-trick of tries.
But just as it looked as if the sparse 3,570 crowd was going to be treated to a one-sided victory, Caledonia gathered themselves. Three Shepherd penalties to a solitary goal by Will Carling shook the home side. Williams's second try, unconverted, like most of Quins' touchdowns yesterday, was quickly countered by the right wing David Officer, with Shepherd converting.
A four-point cushion was hardly what Quins had expected to have by half- time and they set about amending affairs. The arrival of Paul Challinor for the injured Williams saw Carling moving into the centre. Almost immediately the former England captain chipped over the advancing Scots, and Daren o'Leary collected before putting Staples in for his second.
That was matched by a similar unconverted effort from the fly-half Jon Newton five minutes later, a score which heralded the start of a surge by Quins. O'Leary and Staples touched down before Caledonia could get a grip. When they did, their captain McIvor wrapped up a fine break by the centre Paul Rouse.
The ping pong had only just started. Harlequins took their turn at scoring and saw Challinor and Paul take them to the brink of their half-century. Then the ball was in the Caledonian court and after they gained strength from a flurry of replacements, McIvor picked up his second try under the posts, leaving Shepherd with a simple kick.
Caledonia's misery was completed when Jon Kerr looked to have beaten O'Leary to Carling's injury-time chip over the line, but the Irish referee Leo Mayne saw it differently and Quins reached the 50-point mark. Carling managed to convert the try to bring him a 50 per cent return - five out of 10 - from his kicking at goal.
Harlequins: J Staples; D O'Leary, R Paul, G Connolly (D Luger, 79), J Williams (P Challinor, 40); W Carling, H Harries; J Leonard (capt), K Wood, A Mullins, G O Llewellyn, A Snow, R Jenkins, B Davison (M Watson, 37-42), L Cabannes.
Caledonia: R Shepherd; D Officer, P Rouse (J Thomson, 65), A Carruthers, J Kerr; J Newton, P Simpson; T Smith (W Anderson, 42), K McKenzie, D Herrington, S Hamilton (C MacDonald, 65), S Grimes, D McIvor (capt), M Waite, G Flockhart (S Hannah, 65).
Referee: L Mayne (Limerick).
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