For only the second time this season, Seri started a league game on the sidelines and, alongside Aboubakar Kamara, was introduced six minutes after Lacazette had doubled the Gunners' lead.
Moments later, the former Nice midfielder slipped in youngster Ryan Sessegnon who fired in a low cross for Kamara to half the deficit.
And to counteract Claudio Ranieri's plot, Emery took off his French attacker for wantaway midfielder Ramsey ‘to get close’ to Seri [who won all of his duels]; a move that generated boos from some sections of fans at the Emirates.
The 75th-minute tactical tweak, however, paid dividends - in the final third though - as the Wales international got in on the act four minutes after his introduction before Pierre-Emerick Aubameyang capped off scoring to help the Gunners to a 4-1 victory.
“Tactically, we were thinking that in that moment we needed to change to get more balance,” Emery explained.
“Above all else, we know Jean Michael Seri very well and we needed to get a player close to him, to not let him play with the ball very easily. When Aaron Ramsey came onto the pitch, he could do that and can also help us in attacking moments - and he scored.
“The reason for the decision was this and I need to do my work. Every supporter can think different things tactically, but for me today, Lacazette worked very well, scored and he helped us. His reaction was very positive.”
The loss did not help Fulham's cause as they are still placed 19th in the top-flight log, having garnered a meagre 14 points from 21 games.
Since arriving Craven Cottage in the summer, Seri has played 22 times, including a League Cup appearance and he has a goal to his name.
He will hope to have a glorious FA Cup debut when Fulham face Oldham Athletic next Sunday.