Alan Pardew was left breathless after Albion's brilliant 3-2 victory over Liverpool at Anfield.
The Baggies made it through to the Fifth Round after Jay Rodriguez fired a first half brace and a Joel Matip own goal after Craig Dawson's shot.
Liverpool opened the scoring through Roberto Firmnio chipped Ben Foster inside the opening ten minutes.
Mohammed Salah then continued his fire form in front of goal 15 minutes from the end to pull one back for the hosts but Albion held on during an controversial night trailling the video assistant referee system.
The hosts were awarded a controversial penalty in the first half and then the Baggies had a header from Craig Dawson disallowed after Gareth Barry was adjudged to be offside.
"It was a strange game in terms of the VAR system. It was frustrating for us, two calls which went against us, but nevertheless we played some brilliant football," said Pardew.
"I think Dawson's goal in any other scenario would have counted and made the game maybe even more different than it was.
"In the end we've lost three or four players to hamstring injuries which may have been, certainly the first two, down to VAR with how long we were waiting.
"But let's not take away from what it was for West Brom, a great night for us.
"For our fans who were watching in pubs and clubs up and down the country. Brilliant.
"And the fans who were here, it was a special night because we played so well."
Pardew added: "I don't think Liverpool will have any complaints, I think we deserved to win.
"I'm very proud of the players and they should be proud of themselves."