The Rhinos, who have won back-to-back Grand Finals from fifth, trailed 6-4 at half-time in their final league match but dominated the second half to run out comfortable winners and secure a trip to Warrington in the opening round of the play-offs next Saturday.
"I've never finished this high," said McDermott, who left struggling Harlequins to succeed Tony Smith at Headingley three years ago. "I'm very fortunate to be coaching these type of people."
McDermott had the luxury of choosing from a fully-fit squad, with Danny McGuire, Brett Delaney, Jamie Jones-Buchanan and Ryan Bailey all making their comebacks from lengthy injury lay-offs in the last week.
However, they managed to maintain their challenge during the height of their mid-season injury crisis and that, according to McDermott, adds to the sense of achievement.
"We're not slapping our backs too heavily but it's a remarkable effort by the players," he said.
"We've been without some key people for such a long period of time but we've all stuck together through testing times.
"I think we've been good for the majority of the year. I know it seems like we've just started to wake up but we've been in good nick for a while in fairness."
Leeds took the lead thanks to a 95-metre interception try by winger Ben Jones-Bishop and, after conceding a score to Wigan winger Pat Richards just before half-time, dominated the second half, adding further tries through Kallum Watkins, Carl Ablett and Joel Moon.
After leading the table for long periods of the season, Wigan must settle for a fourth-place finish which means a trip to league leaders Huddersfield in next Thursday's opening play-off tie.
The Challenge Cup winners will need a remarkable transformation after finishing their Super League campaign with seven defeats in nine matches but coach Shaun Wane insists he can turn their fortunes around.
"We weren't at out best," he said. "I thought Leeds were outstanding.
"We tested them in small parts of the game but not enough. Leeds have some classy players who know how to win games and I thought they did a job on us.
"It's sad the way it's happened but I know we can play better than that."
Wane brought the majority of his cup-winning team back after resting them a week ago but the Warriors sorely missed their inspirational captain Sean O'Loughlin, who is out for at least four weeks with an Achilles tear.
"Any Super League team would miss him because he's a great player but the fact is he's injured and he's not going to be back next week so we have to deal with it," Wane said.
"We've a big game on Thursday and we will have to make sure we're good for that."
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