The Whites were held to a 3-3 draw by Sunderland in the Premier League Cup, having led by three goals at the half-time break.
Leeds were aiming to get their campaign back on track by kicking off the new year with victory and looked to have done so at the York Community Stadium.
A second half fight back from the Black Cats, however, saw the points shared in Group E of the development tournament.
Head coach Mark Jackson called upon some of Thorp Arch's more seasoned academy starlets with Summerville, Sam Greenwood, Cody Drameh and Kristoffer Klaesson all starting.
They were mixed in with an array of younger players including the likes of 15-year-old Archie Gray.
Leeds have tended to use the tournament to hand experience to their Under-18s along with bedding in those looking for game time in the youth ranks.
It was one of the older players who stole the show in the opening period before making a swift departure at the break alongside Greenwood and Drameh.
Summerville took his time inside the area to guide a well-placed effort into the far corner of the net inside 10 minutes and break the deadlock, giving his side a deserved advantage.
He was in the right place at the right time again a short while later as Max Dean produced some clever control on halfway to set him free one on one.
The Dutchman then saw his hat-trick completed in the 35th minute, following in a Greenwood chance to sweep home a loose ball.
United were in cruise control at the break but with inexperience and changes came mistakes and a halt to the fluidity after the interval.
Ciaran Dunne beat Klaesson at his near post just ahead of the hour and Caden Kelly hauled Sunderland within one goal nine minutes from time.
Leeds - in between the goals - provided some resistance through Dean and substitutes Stuart McKinstry and Jack Jenkins who all went close.
It was the visitors, though, who had the final say on the night to see United's academy give away another lead - an unfortunate theme that has narrated their campaign to date.
Ethan Kachosa was the man to provide the fairy tale finish for the Black Cats, levelling in added time from a swift counter-attack to earn a point for his side.
The draw leaves Leeds third in the group and a point behind Sunderland with two games remaining left to earn qualification into the knockout stages.
Wigan Athletic sit top of the pile on nine points - Leeds travel to face them next week - while Mansfield are now bottom on goal difference.
United will turn their attention back to Premier League 2 action on Monday afternoon, visiting West Ham United in an attempt to haul themselves away from the relegation zone after a 10-game winless run in the league.
Leeds United: Klaesson, Drameh (Moore 45), Ferguson, Coleman, Littlewood, Debayo, Summerville (McKinstry 45), Gray, Dean, Greenwood (Jenkins), Miller. Subs: Van Den Heuvel, Mullen.
Sunderland: Carney, Kachosa, Newall, Sohna, Younger, Xhemajli, Dunne, Scott, Taylor, Kelly, Dyce. Subs: McIntyre, Johnson, Jones, Gyimah.