On-the-whistle report: Kieran Sadlier the hat-trick hero ... Rotherham United 5 Manchester City Under-21s 0

The Millers eased away from their young visitors with five second-half goals in a tie which brought the debut of manager Paul Warne's teenage son, Mackenzie.

Rotherham, after three Group E wins from three in this tournament, will now have home advantage when the knockout phase begins.

Sadlier's treble and goals from Will Grigg and Jake Hull and Kieran Sadlier, 2 helped Warne's men stretch their unbeaten run in all competitions to ten games.

Hakeem Odoffin had a 12th-minute shot saved by Cieran Slicker in an opening period in which neither side dominated and soon afterwards there was a long delay when Viktor Johansson required treatment.

Happily, the Millers goalkeeper, who had raced from his lined to clear a Manchester ball forward and collided with teammate Hull, was able to continue.

City's youngsters were neat, nimble and quick to break but it was the home team who threatened again on 24 minutes as Tolaji Bola headed Jacob Gratton's cross wide.

Seconds later, at the other end, Shea Charles let fly and his fierce shot was deflected for a corner.

Hull, four days after his 20th birthday, headed over on the half-hour mark in a contest hardly brimming with clear-cut chances.

A small crowd was housed entirely in the East Stand where a smattering of City fans were also gathered on a mild autumn evening.

The visitor's Liam Delap did well to create space for a shot but then blazed off target and neither set of supporters had had a great deal to cheer about as the teams went in goalless at the break.

With Sunderland up next at New York in a League One promotion clash, Warne chose to rest most of his main men and field a young side.

There were starts for Hull, Gratton and Curtis Durose, who have all come though the Millers' youth set-up, while Warne Junior and other Academy kids Jerome Greaves, Sam Greenhouse and Ciaran McGuckin were on the bench.

Mickel Miller and Freddie Ladapo were the only starters who'd seen action at MK Dons last Saturday.

Ladapo was taken off at the interval and it took his replacement, Grigg, only six minutes to break the deadlock as the loan striker turned in Sadlier's shot.

Five minutes later, Grigg was guilty of losing possession to close too his own goal and Kayky wasted a golden 56th-minute opportunity to equalise by firing over.

The match was opening up now and, after Sadlier had missed in similar fashion to Kayky, City broke through the game's best player, James McAtee, who was thwarted by Johansson, with Richard Wood, the oldest man on the pitch on a night of youth, blocking Nico O'Reilly's follow-up.

Sadlier went one on one with Slicker on 60 minutes, with the City keeper winning that duel, then made amends three minute later by converting a penalty awarded for a foul on Josh Kayode.

Warne junior and McGuckin, another debutante, had been part of the action for only a minute when Hull added the third, heading home from a corner for the second time in his three Trophy appearances.

McGuckin's header set up Sadlier for an 81st-minute volley and the midfielder then crowned his and Rotherham's evening with a quality strike from a 90th-minute free-kick.

Rotherham (3-5-2): Viktor Johansson; Jake Hull, Richard Wood (Mackenzie Warne 65), Tolaji Bola; Jacob Gratton, Curtis Durose (Ciaran McGuckin 65), Kieran Sadlier, Hakeem Odoffin, Mickel Miller; Freddie Ladapo (Will Grigg H-T), Josh Kayode. Subs not used: Josh Vickers, Wes Harding, Sam Greenhouse, Jerome Greaves.

Man City (4-1-2-3): Cieran Slicker; Rico Lewis, Finley Burns, Luke Mbete, Josh Wilson-Esbrand (Oscar Tarensi-Cordon 87); Romeo Lavia; Shea Charles, James McAtee; Oscar Bobb, Liam Delap (Nico O'Reilly H-T), Micah Hamilton (Kayky H-T). Subs not used: Mikki Van Sas, Jadel Katongo, Kwaku Oduroh.

Goals: Grigg 51, Sadlier 63 pen, 81, 90, Hull 66 (Rotherham).

Referee: Samuel Barrott (West Yorkshire).

Attendance: 1,908 (120).