Former ballboy Micah Hamilton and fellow youngster Oscar Bobb struck as a much-changed Manchester City ended the Champions League group stage with a 3-2 win at Red Star Belgrade.
Kalvin Phillips also joined the two 20-year-olds on the scoresheet with a late penalty after manager Pep Guardiola rotated his squad for the Group G dead rubber at the Rajko Mitic Stadium.
Manchester-born academy product Hamilton marked his debut with a superb strike in the 19th minute before Norwegian Bobb, filling in for compatriot Erling Haaland up front, added the second after 62 minutes.
Hwang In-beom pulled one back but Phillips gave City breathing space with his first goal for the club after a foul on Hamilton before Aleksandar Katai headed a late home consolation.
The result meant holders City, who had already secured top spot, finished the group phase with a maximum haul of 18 points while winless Red Star ended bottom.
With City facing Crystal Palace before travelling to Saudi Arabia for the Club World Cup next week, Guardiola not only gave chances to Hamilton and Bobb but brought in fringe players such as Stefan Ortega and Phillips.
In all he made nine changes and, initially, intensity was lacking as Red Star carved out the first opportunity with Osman Bukari's shot being blocked by John Stones. Yet City still controlled most of the possession and Hamilton took full advantage of their first serious attack.
Jack Grealish picked out Matheus Nunes and the Portuguese prodded on for Hamilton, cutting inside from the right, to take up the attack.
Hamilton raced into the area and beat Red Star captain Aleksandar Dragovic on the outside before lashing a shot into the top corner from a tight angle.
The hosts responded with Kosta Nedeljkovic turning inside the box and curling narrowly over but City threatened again as Bobb had an effort blocked.
Hamilton almost created another goal for Bobb when he fired in a dangerous low ball from the right but the latter could not make contact at the far post. Phillips, making a rare start, then shot wide. Hamilton went close again early in the second half when he curled a low effort just wide but City needed Ortega to keep them level.
The German first produced a good reaction save to keep out a Cherif Ndiaye volley at close range and then pushed away a firm strike from distance from Guelor Kanga.
Bobb then took centre stage as he doubled City's lead just after the hour. He picked up possession from Rico Lewis and opted against the return pass, instead wrong-footing the defenders with a weaving run and sliding a low finish inside the far post.
Red Star rallied and, after Jovan Mijatovic hit the post, Hwang beat Ortega with a low strike to reduce the deficit after linking up with Bukari.
Yet Phillips made no mistake from the spot five minutes from time after Hamilton was brought down by Nasser Djiga and that proved decisive as Katai headed a second Red Star goal in stoppage time.
