Mason Greenwood opened his Manchester United account in style as the 17-year-old secured Ole Gunnar Solskjaer's men a 1-0 win against Astana in their Europa League Group L opener.
Back in the competition for the first time since lifting the trophy two years ago, the Red Devils' gruelling road to the final in Gdansk, Poland, next May got off to a surprisingly uncomfortable start with the only goal coming in the 73rd minute against the perennial Kazakhstan champions.
"It's good for (young players) to have the opportunity to play in these games, they have to use that to work hard and play more games," Manchester United midfielder Nemanja Matic said.
"They want to prove they deserve to wear the shirt, they are the future of the club."
Arsenal cruised to a 3-0 win in Germany with their teenage winger Bukayo Saka scoring his first goal for for the club as they beat 10-man Eintracht Frankfurt.
Joe Willock put the Gunners ahead late in the first half before Londoner Saka, 18, added a second in the 85th minute and Pierre-Emerick Aubameyang slotted home a third to secure all three points.
The win put Unai Emery's side top of the Group F ahead of Standard Liege who beat Portugal's Vitoria Guimares 2-0.
Wolves won all six of their qualifiers but were beaten in their Group K opener by Sporting Braga.
Forward Ricardo Horta bagged his fifth goal of the season to snatch a 1-0 opening win for the Portuguese at Molineux.
In Group E, Socceroos midfielder James Holland scored a 45th minute winner for his Austrian side LASK at home to Norway's Rosenborg, and Dutch club PSV Eindhoven edged out Portugal's Sporting Lisbon 2-1.
Another Socceroos midfielder in Tom Rogic was an unused sub in Celtic's 1-1 draw with Rennes in France.
Glasgow Rangers faired better than their city rivals with Sheyi Ojo producing a moment of magic to beat Dutch giants Feyenoord 1-0 at Ibrox, while Porto earned a 2-1 win over Young Boys also in Group G.
Record five-time winners Sevilla thrashed Qarabag 3-0 in Baku to top Group A.
Swiss side Basel hammered Krasnodar 5-0 at home and Getafe beat Trabzonspor 1-0 in Group C's other game.
Roma thrashed Istanbul Basaksehir 4-0 while Borussia Monchengladbach fell to Austrian side Wolfsberg by the same scoreline.
PSV Eindhoven beat Sporting Lisbon 3-2 in their Group D opener while Dynamo Kiev and FC Copenhagen scored 1-0 wins over Malmo and Lugano respectively in Group B.