REPORT: Wigan Athletic 7 Leicester City Under-21s 1: Tics in seventh heaven as they start Wembley trail
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The visitors had actually taken the lead on the half-hour - after Scott Smith had hit the bar for Latics with a cross-shot that deceived the Leicester goalkeeper.
Liam Morrison gave the ball away and Leicester broke, resulting in Arjan Raikhy firing home an unstoppable shot into the top corner from 25 yards.
The lead lasted barely two minutes, however, as Liam Shaw was manhandled at a Wigan corner, which saw referee Scott Simpson point to the spot.
Up stepped up Magennis, and parity was restored.
Only a brilliant save from Brad Young prevented Jordan Jones putting Latics ahead before the break, with a lovely cross from Smith somehow evading the two attackers desperately trying to get on the end of it.
Harry McHugh took over from Morrison, and Latics were ahead within 30 seconds of the restart.
Jonny Smith supplied the trickery and cross from the right, and Magennis supplied the cool finish at the near post.
The most popular goal of the night occured on 57 minutes, when a Jonny Smith corner was guided back in by Charlie Hughes for Lang to nod home from a yard - his first goal since his winner at Huddersfield on September 13 last year.
Two minutes later it was 4-1, with Magennis' looping header finding its way in via the far post and the desperate efforts of Young to keep it out.
Callum McManaman, Chris Sze and Josh Stones replaced Jonny Smith, Lang and Magennis for the last half hour.
But Stones showed there would be no let-up for the Foxes defence by rattling the crossbar within seconds of his introduction.
McHugh smashed a loose ball home from a couple of yards to open his senior account with 18 minutes left to make it 5-1.
And a superb solo goal from Sze made it six with five minutes to go, before Stones notched his first professional goal deep into stoppage-time to put the icing on the cake.