Yarmolenko appeared as a second half substitute and opened the scores in a 2-1 win for the Hammers against Aston Villa at the London stadium.
The Ukraine international sunk to his knees in tears after the goal and was mobbed by his teammates while both sets of supporters applauded.
Yarmolenko was making his first appearance for David Moyes' side since his country's invasion by Russia, having been granted a compationate period of leave.
Yarmolenko is Ukraine's second highest goalcorer of all-time with 44 goals from 106 caps.
The former Borussia Dortmund attacker remains grateful for the love he was shown in what has been a challenging period.
"What happened today, it was so emotional for me," the 32-year-old told West Ham's media channels.
"You know the situation in my country, it's so difficult for me, at this moment, to think about football because every day in my country, Russia's army kills Ukrainian people. So, it was so emotional.
"To be honest I don't know what to say, it's just so emotional. I just want to say thank you to my team-mates, who support me all the time, every day.
"To the West Ham fans, who support me, who support the Ukrainian people, I also want to say thank you.
"I want to say thank you to all British people, because we feel that you support us.
"For me it's really important to feel support from the manager, from team-mates, and from the fans. When I feel it, I give everything for the fans and for the club."
