Chelsea were made to sweat for a spot in the fifth round after defeating Hull City 2-1 at the KCOM Stadium.
The visitors opened a two-goal lead through Michy Batshuayi and Fikayo Tomori.
Kamil Grosicki reduced the deficit for Hull in the final 15 minutes, but the Blues were able to hold on for the win.
For the second round in a row, Tottenham Hotspur will feature in a replay after playing to a 1-1 draw with Southampton.
Hueng-min Son gifted Spurs the lead on 57 minutes, but Southampton secured themselves a replay thanks to Sofiane Boufal's 87th minute strike.
Goals from Muhamed Besic and Oliver Norwood guided Sheffield United to a 2-0 victory over Milwall on Saturday afternoon.
Kelechi Iheanacho's fourth-minute strike was enough to hand Leicester City a 1-0 win over Championship outfit Brentford.
Bafana Bafana midfielder Kamohelo Mokotjo played 45 minutes for the home side.
The big shock of the round came at the London Stadium as West Bromwich Albion defeated West Ham United 1-0.
Conor Townsend got the game's only goal after nine minutes, while West Brom also finished the game with 10 men after Semi Ajayi was sent off in the final 20 minutes.
Reading 1-1 Cardiff City
Burnley 1-2 Norwich City
Coventry 0-0 Birmingham City
Newcastle United 0-0 Oxford United
Portsmouth 4-2 Barnsley