It ought to have been the perfect day for Southampton, instead it turned into a right royal coronation. After seeing Brian McDermott's side slip up and bitter rivals Portsmouth relegated, a memorable three-hour spell could have been rounded off in style with the cessation of a seven-year Premier League exile.
Two out of three isn't bad. For much of a compelling contest, it appeared the trio of elements would come together for Nigel Adkins' side. But after taking the lead after 46 seconds, they were pegged back by spirited hosts, who kept their slim play-off hopes alive thanks to a stunning winner 13 minutes from time, midfielder Merouane Zemmama curling home a 25-yard free-kick after Jose Fonte had been harshly judged to have tugged back Southampton-born Lukas Jutkiewicz. The cheers from Royal Berkshire as Reading were confirmed as champions thanks to their point at home to Crystal Palace, could almost be heard on a rain-sodden Teesside.
For Southampton, the promotion party will have to wait at least until tomorrow night, when West Ham travel to Leicester City. Anything but victory for the London club will see the Saints marching back into the top flight. Should it go to the final day, the fixture computer has been kind to Nigel Adkins' side, who welcome the already relegated Coventry.
"We send our congratulations to Reading, but from our point of view promotion is still in our own hands," Adkins insisted. Should West Ham take matters to the final day, given their superior goal difference, a point at home to the doomed Sky Blues should be enough to seal back-to-back promotions for the south coast club. A win definitely would.
Insisting that he expected West Ham to win on Monday, Adkins added: "There was a chance there for us, but we must now make sure we win in front of 32,000 of our fans roaring us on this Saturday."
Billy Sharp gave Southampton the lead inside the first minute with a far post tap in from Rickie Lambert's square pass.
But despite enjoying long periods of possession, Southampton couldn't find the decisive second goal, leaving them open to a well-struck equaliser from Nicky Bailey.
In a no-holds barred second half, Zemmama completed the comeback with a perfectly placed set-piece to leave Tony Mowbray's side needing to win at Watford on Saturday and hope Cardiff slip up to see them sneak into sixth place.
Tony Mowbray insisted: "We showed our fighting qualities, and we deserve enormous credit. It helps when a side comes and attacks us like Southampton did. We've kept our season alive to the last 90 minutes."
Middlesbrough (4-4-2) Steele; McMahon, Hines, McManus, Hoyte (Bennett, 40); Haroun, Robson (Williams, 59), Bailey, Zemmama; Jutkiewicz, McDonald (Main, 59).
Southampton (4-4-2) Davis; Butterfield, Fonte, Hooiveld, Fox (Schneiderlin, 84); Chaplow (Do Prado, 62), Cork, Hammond, Lallana; Lambert, Sharp.
Referee Tony Bates.
Man of the match Bailey (Middlesbrough).
Match rating 7/10.