In-form Crysencio Summerville rescued West Ham in extra time as they avoided an FA Cup shock at League One Burton.
The substitute struck in the 95th minute to save the visitors with his sixth goal in seven games after they laboured at Pirelli Stadium.
Freddie Potts was sent off for a reckless challenge on Julian Larsson in the first half of extra time but the Hammers survived to reach the fifth round.
Manager Nuno Espirito Santo made 10 changes and the disjointed visitors struggled against a team 47 places below them and fourth-bottom in League One.
A plane pulling a banner protesting against West Ham owner David Sullivan and vice-chair Karren Brady flew over the stadium before the game and a limp performance would have done little to change the mood.
They may have won three of their past five Premier League games but the underlying frustration and anger with the running of the club remains, with the Hammers third-bottom of the table.
They struggled against an organised, disciplined but limited Burton who matched them for a forgettable 90 minutes.
Summerville, a late second-half substitute, finally offered a rare moment of quality early in extra time when he cut inside and his shot brushed Terence Vancooten to beat goalkeeper Brad Collins from the edge of the area.
Potts was then dismissed for a dangerous challenge on Larsson and Summerville missed a golden late chance as West Ham held on, despite Burton pressure.
West Ham analysis: Worry over Nuno’s squad depth after nervy win
It was a let-off for the Hammers who were poor, sloppy and lacked imagination.
Nuno’s 10 changes looked like it could backfire with Burton the better side for long spells.
A more dynamic side would have taken advantage of the visitors, who needed their man of the moment Summerville to save them from at least going to penalties.
The travelling fans, who chanted “sack the board” early on after the plane circled the ground would have had more ammunition if Burton had sprung a shock.
Ultimately they have progressed – but it was nervy and West Ham had to ride out some late Burton pressure and chances.
Nuno can claim it was mission accomplished, he rested several key players and West Ham still went through. But it does not offer much comfort over the depth of his squad before the relegation run-in.
