Louis Reed's goal in the 80th minute at Turf Moor completed a comeback 2-1 win for the League One team in the fourth round after they'd gone behind in the first half on Saturday.
As giant-killings go, it might not be as spectacular as non-league Macclesfield's victory against title holders Crystal Palace last month - but it is another major shock result in soccer's oldest knock-out competition.
An increasingly painful season got worse for Burnley after the humiliation of being dumped out of the Cup against a team from two divisions lower.
Mansfield are mid-table in League One and even against a Burnley team that had won just two of their previous 18 games, went into the match as underdogs.
And when Josh Laurent scored in the 21st, it looked like the home team would book their place in the last-16.
That was until a second-half fightback from Mansfield sparked by Rhys Oates' equaliser eight minutes after the break and Reed's late winner.
It's been a very good week for Pep Guardiola's Man City who've closed the gap on Premier League leaders Arsenal to four points and got past local fourth-tier rivals Salford 2-0 to make the fifth round.
Their four-pronged trophy pursuit is still in good shape after victory against the little side co-owned by Manchester United greats David Beckham and Gary Neville.
City beat Exeter 10-1 in the last round and Salford might have feared a similar outcome when Alfie Dorrington scored an own goal in the sixth minute, but City had to wait until the 81st to score again through Marc Guehi.
Burton, fighting against relegation in the third-tier, went toe-to-toe with top-flight West Ham, forcing the game into extra time at the Pirelli Stadium before going down 1-0 to a 95th-minute goal from substitute Crysencio Summerville.
A red card for West Ham's Freddie Potts six minutes later meant there were still some nerves before the final whistle was blown.
There was relief all round for West Ham, who are fighting a relegation battle in the Premier League.
Elsewhere, Socceroo Mohamed Toure got on the scoresheet again as Norwich beat West Brom 3-1, while Southampton needed extra time to beat Leicester 2-1.
17°C