Semi Ajayi made his maiden appearance for West Bromwich Albion in their 1-1 draw against Rotherham United in a pre-season friendly game on Tuesday.
On Saturday, the 25-year-old midfielder completed his move to the Hawthorns, signing a four-year contract with the side.
The Nigeria international was handed a starting role against his former club but endured a difficult debut appearance on his return to the New York Stadium.
Ajayi’s late challenge on Freddie Ladapo led to a penalty and the Anglo-Nigerian calmly slotted home his effort to give Paul Warne’s men the lead.
Substitute Dara O’Shea rescued the day for Slaven Bilic’s side after heading home Filip Krovinovic’s cross for the equalising goal.