Lukaku was a second-half introduction, replacing the injured Kai Havertz at the London Stadium.
The Belgian, who is only returning from injury, had little impact as the Hammers scored two second-half goals to come from two goals down to win.
Speaking after the match, Tuchel acknowledged it was his fault as Lukaku still lacks match fitness.
“It’s my fault,” he said. “I don’t think he is ready for 45 minutes physically but still we decided to bring him on for his height because we lost Kai.
“Kai had a crucial role in defending set-pieces, which is a huge threat from West Ham, so this is on me. I took the decision so it’s my responsibility,”
The chelsea loss kicked Manchester City and Liverpool to the Top and Second of the table following their victories over Watford and Wolves.
The Blues lost for the fifth time in the league under Thomas Tuchel, and slid to third place.