After substitute Saido Berahino gave West Brom 67th-minute lead, goals from Jonathan Kodjia and Kieran Agard put Bristol City in charge, only for Morrison to secure a 2-2 draw at the death.
Aston Villa’s wretched season continued as they were taken to a replay by fourth-tier minnows Wycombe Wanderers following a 1-1 draw at Adams Park — their 16th successive game without victory.
Eleven points adrift of safety at the foot of the Premier League table, Villa took a 22nd-minute lead through Micah Richards, only for Joe Jacobsen to equalise with a penalty early in the second half.
Villa captain Richards went over to speak to frustrated Villa fans at the final whistle and manager Remi Garde said: “It was brave of him to do that.
“As professionals, we have to face our responsibilities — not only Micah, me and all the players.”
Bolton Wanderers, bottom of the Championship and at risk of bankruptcy, narrowly escaped succumbing to the day’s biggest shock as Darren Pratley’s scrappy 87th-minute goal earned them a 1-1 draw at fifth-tier Eastleigh.
The lowest-ranked team left in the tournament, Eastleigh had gone ahead in the 51st minute via an own goal by Bolton’s French defender Dorian Dervite.
Manchester United face lower-league opposition later on Saturday in the form of third-tier cup specialists Sheffield United, who reached the League Cup semi-finals last season and the FA Cup last four the year before.
Liverpool were taken to a replay by fourth-tier Exeter City on Friday, Brad Smith’s 73rd-minute equaliser sparing Jurgen Klopp’s youthful side from an ignominious exit. [myad]
