The Palace No.23 came on at half-time with the Three Lions 6-0 ahead against San Marino. They went on to win 10-0.
Gallagher became the first player to earn an England call-up while representing Palace since Aaron Wan-Bissaka in 2019, however went one step further than the Academy graduate by taking to the turf at the Stadio Olimpico di Serravalle.
He sat in his usual box-to-box domestic role but was able to roam further forwards regularly - hitting the post in the 70th-minute and being fouled by Dante Rossi, who was then sent off, to win a free-kick England scored their eighth from - with the Three Lions flexing their attacking muscles against the 210th-ranked San Marino.
Victory confirmed their qualification for the 2022 World Cup in Qatar. And it was a night to remember for the national side, with several debuts and first goals scored; this was the first time they scored 10 goals in a single game since 1964.