On his introduction as a substitute for Kai Havertz after 76 minutes, the 22-year-old received generous applause from the Palace fans who voted for him as their Player of the Year last season when he was on loan in south London.
However, he did not allow his past loyalties to get in the way of his current job as he fired home a stunning late winner to give Graham Potter a winning start in his first league match in charge of the Blues.
It was our second match in a row against the Eagles in which a crucial goal was scored by a player who once played for them. In the FA Cup semi-final at Wembley last April, the match was goalless after 65 minutes when Ruben Loftus-Cheek broke the deadlock with a venomous strike against the club where he spent the season on loan in 2017/18.
Another player who found the net against his former team in our last campaign was N’Golo Kante who marked his return to the King Power Stadium with a spectacular solo goal in our 3-0 win over Leicester City. It was the second time the French midfielder had come back to haunt his former fans after his long-range effort in our 2-1 victory at the King Power in September 2017.
Like Gallagher on Saturday, Tammy Abraham opted not to celebrate when he opened the scoring in our 2-1 win over his former loan side Aston Villa in December 2019, seven months after he helped the Birmingham club secure promotion through the Championship play-offs.
The same could not be said about Fikayo Tomori when he scored the decisive goal in our 2-1 victory over Hull City in the fourth round of the FA Cup a month later. It was one of only two goals scored by the Academy graduate in 27 senior appearances for the Blues and his delight was clear to see as he celebrated in front of the Chelsea fans at the KCOM Stadium where he had played for the Tigers on loan in 2017/18.
Olivier Giroud did not score a Premier League goal against Arsenal after moving across London to join Chelsea in 2018 but the French striker was on target when we met the Gunners in Baku the following year as he opened the scoring in a 4-1 victory in the Europa League final.
There are a couple of other ex-Gunners who caused some damage against their former club in the Premier League. Cesc Fabregas lobbed past former Blue Petr Cech in a 3-1 win on the way to us lifting our second league title in three seasons in 2016/17 while Nicolas Anelka slammed home a brilliant long-range strike when we won 4-1 at the Emirates Stadium in May 2009.
It was one of three goals scored by the much-travelled Frenchman that season at his former home grounds as he also struck in a 3-1 win at Manchester City and 2-0 victory at Bolton Wanderers en route to claiming the Premier League Golden Boot with 19 goals.
Finally, a word of mention for Frank Lampard who declined to celebrate after scoring a late equaliser against Chelsea when he played for Manchester City in a 1-1 draw in September 2014. Most Blues supporters probably forgave him for that scoring transgression, however, on account of his club-record 211 goals which included seven against his former side West Ham United.