Edwin van der Sar produced the first save of the day fingertipping a header from Marcus Bent over the bar.
But Kirkland was soon in action dealing from a trademark Ronaldo free-kick which beat the wall from outside the box
Backed by a full house in thundery conditions, Wigan made a positive start with Michael Brown giving Van der Sar an early test.
Jason Koumas twice failed to hit the target, firing one wide and skying the other over the bar. Rio Ferdinand headed over from a Michael Carrick corner and Scholes rattled one wide when another corner was only partly cleared.
The goal United needed came when Wayne Rooney was brought down by Emmerson Boyce and the referee had no hesitation in pointing to the spot.
Ronaldo made no mistake hammering in goal number 41 of his season after sending Kirkland the wrong way.
Scholes, who had been booked earlier for a foul on Wilson Palacios, was lucky not to find himself in big trouble after bringing down the same player, as the referee settled for a stern word.
It fired Wigan up and Bent was inches away when he fired into the sidenetting. Ronaldo then thundered another free-kick in with Kirkland easing it over the bar.
United had strong penalty claims when Scholes went down under pressure from Titus Bramble, with Mr Bennett inexplicably awarding a corner, not a second spot-kick.
The Reds Devils were hunting the killer goal and only another brilliant save from Kirkland denied Rooney.
Giggs then came on to equal Sir Bobby Charlton's United appearance record and in a fairytale finish he wrapped it up after Rooney had sent him clear.