Harlequins 22 Leeds Rhinos 42: Rhinos rally to underline they can live without their top names
Missing a host of international stars on England duty, the visitors opened up 16-0 and
34-12 leads and then held off two rallies from Harlequins.
And McClennan was eager to hail the efforts of some of his stand-ins.
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Hide AdHe said: "It was a great effort. It was a great opportunity for the players to grab hold of the situation and get something out of it. All of the players that I brought in gave a very good account of themselves.
"There was a different chemistry out there.
"The players took a lot of ownership for how we were going to play.
"There was a lot of maturity on display and I am delighted."
After a slow start the contest burst into life on the 10-minute mark when Lee Smith pounced on Tony Clubb's fumble to race half the field to score.
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Hide AdWhen Paul McShane and Brent Webb added further tries inside 25 minutes, things looked ominous for the hosts.
But Quins gave themselves a lifeline when Luke Dorn took Danny Orr's pass to score and then Orr added a penalty on the hooter. After a further try by Dorn shortly after the interval, it was game on.
Leeds got back down to business as Luke Ambler touched down, and when Smith claimed his second the nerves had been calmed.
Carl Ablett then added a further Rhinos score, holding onto a flat pass from Webb as they passed the 30-point mark, and a canter looked on the cards.
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Hide AdBack came the hosts, with quick-fire tries from David Howell and Luke Gale livening up the contest once more.
With the London club on the front foot, the Rhinos buckled down again, with Smith booting a penalty to stretch the lead.
And fittingly it was Smith who had the final word, the winger claiming his third try as Leeds earned a deserved victory.
For Quins coach Brian McDermott, it was a case of ruing the slow start from his side.
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Hide AdHe said: "We started the game in a terrible fashion and we were always trying to catch up."
Harlequins RL: Dorn, O'Callaghan, Clubb, Howell, Sharp, Gale, Randall, Wilkes, Orr, McCarthy-Scarsbrook, Williamson, Temata, Melling. Substitutes: Ellis, Krasniqi, Ward, Esders.
Leeds Rhinos: Webb, Donald, Delaney, Senior, Smith, Ablett, McShane, Leuluai, Buderus, Ambler, Kirke, Pitts, Clarkson. Substitutes: Diskin, Amor, Eastwood, Bush.
Referee: J Child (Dewsbury).