Republic of Ireland international Callum Robinson set up West Brom's winning goal as the Baggies edged Sheffield United 1-0 at The Hawthorns in their first round Carabao Cup tie.
Substitute Karlan Grant's 73rd-minute effort – just three minutes after coming on – secured a tie at Sky Bet League One Derby in a game full of chances and a sprinkling of Irish internationals.
Robinson was prominent throughout in the Baggies attack, with Dara O'Shea starting at centre-half for the winners and Jayson Molumby a second-half substitute.
The visitors were captained by John Egan, with loan signing Ciarán Clark introduced with 20 minutes remaining.
United, who made five changes from Saturday’s 2-0 win against Millwall, could have been 2-0 up in the opening minutes.
Rhian Brewster drilled against the foot of the post and debutant Oliver Arblaster’s follow-up was blocked by goalkeeper Alex Palmer, one of 10 Albion changes from Monday’s 1-1 draw against Watford.
Albion’s Alex Mowatt sidefooted wide and Adam Reach delayed shooting before full debutant Reyes Cleary’s shot was smothered by goalkeeper Wes Foderingham.
United forward James McAtee then blazed high and wide, while Cleary should have done better in a one-on-one, but Foderingham smothered his low drive.
Another Albion chance went begging when Reach’s shot was palmed away.
Ex-United forward Robinson’s shot on the turn was turned aside by Foderingham, before Reda Khadra had two efforts – one saved and the rebound wide.
Foderingham denied Albion again when his superb reflex save foiled Reach’s bullet header.
Robinson and Matt Phillips then both hit the top of the crossbar with spectacular shots.
The Baggies eventually made the breakthrough when Grant nodded home Robinson’s cross for his second goal in four days, before departing injured.