The 19-year-old was named among the substitutes for Dortmund's clash with TSG Hoffenheim but was introduced in the 31st minute for the injured Filippo Mané, arriving with his new side already toiling.
Hoffenheim led 2-0 by the 53rd minute, only for Dortmund to launch a spectacular comeback driven by substitute Fábio Silva and striker Serhou Guirassy, levelling the score at 2-2. Nwaneri then settled the contest in the 87th minute, collecting the ball in midfield, exchanging a one-two with Silva down the left and whipping a low cross into the box that Albian Hajdari turned into his own net.
It capped a rapid introduction to life in Germany for Nwaneri, who broke through at Arsenal during the 2024/25 season, scoring nine goals and adding two assists in 37 competitive matches. His game time reduced significantly last season, limited to six league appearances before a January loan to Marseille yielded two goals and an assist in nine games.
Arsenal confirmed his loan move to Dortmund earlier last week, with Sky Sport Germany reporting the north London club holds the option to recall him as early as January.
Arsenal boss Mikel Arteta addressed the recall clause ahead of Sunday's match against Chelsea, choosing not to dwell on the specifics of Nwaneri's future.
"We'll see — for Ethan the focus now is on playing in a fantastic club environment, with the Champions League in sight, and putting all his talent at Dortmund's service, then we'll see what happens," Arteta said. The midfielder remains under contract at Arsenal until the summer of 2030.
A reunion between club and player could come sooner than expected, with Arsenal set to face Dortmund in the Champions League on November 24. Arteta confirmed the fixture could see Nwaneri line up against his parent club depending on the recall clause's status by then.
"It is a possibility now, the door is open and the rules differ from the Premier League," Arteta said.
Nwaneri's decisive intervention against Hoffenheim means he could soon be pushing for a starting role under Dortmund's coaching staff, with the club's Champions League campaign beginning on Tuesday against Villarreal.