Stephane Sessegnon scored an extra-time winner to help Sunderland knock brave Middlesbrough out of the FA Cup.
With a penalty shoot-out looming, the Benin international struck from 15 yards out to send his side through.
Jack Colback put the visitors into a first-half lead with a left-footed strike, before Lukas Jutkiewicz pounced on a loose ball to level.
Martin O'Neill's side will now play Arsenal in the fifth round at the Stadium of Light.
After a slow start, the home side began to press and Sunderland goalkeeper Simon Mignolet needed two attempts to grab former Black Cat Julio Arca's dipping effort.
But just as the hosts sensed they were gaining the upper hand, the visitors hit back in devastating style to take the lead just before the break.
Fraizer Campbell, back in the starting line-up, did well to lay off a long ball into the path of Colback, who controlled instantly before smashing a left-foot volley home off the underside of the bar.
Tony Mowbray's men might have been back in the game almost immediately, but Phil Bardsley cleared Tony McMahon's drive off the line.
Middlesbrough dragged themselves back into the tie when former Coventry man Jutkiewicz was first to react to a loose ball inside the penalty area, and planted a firm right-footed shot past Mignolet to level.
Bardsley's deflected piledriver came back off the post as Sunderland looked for a winner, but the tie went into extra time.
Boro looked the more threatening as the extra 30 minutes started, but their fate was sealed in the 112th minute when Sessegnon drilled home from 15 yards after the ball broke to him to snatch victory for Sunderland.
Middlesbrough manager Tony Mowbray:
"The overriding emotion is disappointment, of course. It's a game we haven't won and somewhere along the line, statistics will be used to say we haven't won since Boxing Day, as I am hearing a lot at the moment.
"It's little consolation. The bottom line is when you go to extra-time, you have got to come out winning the football match, not having any consolation that you might have done okay in the game.
"We didn't win it and Sunderland found a way to win it tonight."
Sunderland boss Martin O'Neill:
"Arsenal will be pretty pleased that we have gone into extra-time. We will try to get ourselves ready for that game.
"The cup game will take care of itself the week after.
"The penalty-kicks were a concern because it's a lottery. I obviously thought The penalty-kicks were a concern because it's a lottery. I obviously thought it was going to go that distance because the two teams were tiring.
"I know they were pressing as the ball broke down, but I am pleased from a selfish viewpoint that it didn't go to penalties."