27 hours ago
Leeds 28 - 16 Harlequins
Great Britain stand-off McGuire crossed the line twice in the first half to sandwich a score from New Zealand Test full-back Webb and help Leeds establish a 20-4 interval advantage.
Webb emulated his team-mate three minutes after the restart when he completed his brace but Rhinos could never rest easy against a spirited Quins side who dominated for long periods in the second half.
The Londoners were ultimately left to pay for a dismal opening period which saw Leeds power 12-0 ahead with little more than 10 minutes played.
McDermott, the former Bradford Bulls prop who quit his post as assistant to Rhinos coach Tony Smith midway through last season, must have feared the worst at that point.
Quins only had themselves to blame for the score which handed Leeds an eighth-minute lead.
Chris Melling, a player whose pedigree has never been in doubt having risen through the ranks at Wigan Warriors before moving to the capital during the close-season, inexplicably dropped the ball 20 metres from his own line.
McGuire needed no second invitation to collect possession and scamper over for the easiest touchdown of this or any other season.
Leeds began to move quickly through the gears, keeping the ball at every opportunity with McGuire at the heart of all their most promising attacks.
And they extended their lead in the 11th minute when McGuire