As the evening wore on Antonio Conte resembled an increasingly disappointed teacher, apparently saddened by his class’s failure to absorb the basic lessons he had so painstakingly drilled into them. The Tottenham manager did not look entirely surprised when his worst fears were realised and, deep in extra time, 19-year-old Josh Coburn stepped off Middlesbrough’s bench and scored a fine, richly deserved winner for Chris Wilder’s impressive side. Admittedly Spurs – and Harry Kane in particular – were far from their best, considerable credit must go to a meticulously organised Middlesbrough and, in particular, Jonny Howson, who shone in a defensive midfield role. Although Kane had a second half goal disallowed for offside, Championship Boro – who beat Manchester United on penalties at Old Trafford in the fourth round – finished the stronger side, suggesting they would not be out of their depth in the Premier League. Wilder jokes that Conte likes to copy his tactical blueprint, and, true to form, two managers who enjoy a decent rapport configured their teams in three at the back, wing-back propelled, formations. Wilder, though, had taken the precaution of deploying Howson in a deep lying midfield role and Howson initially enjoyed a degree of success in helping his defence thwart Kane and company. Conte’s craving for silverware dictated Kane was never going to be rested on a night when Tottenham’s manager made no alterations to the team which had started the 4-0 win at Leeds last Saturday. Wilder’s overriding priority is promotion but he regards the twin pursuit of a play-off place and the FA Cup as far from incompatible and duly started a strong side in front of more than 30,000 at the Riverside. Boro fans had their hearts in their mouths as Conte’s wing-backs, Matt Doherty and Ryan Sessegnon, combined in a fluent attacking move which concluded with Sessegnon creating a chance which Kane would surely have polished off but for Dael Fry’s last-ditch interception. That apart, the first half was not exactly replete with chances as a disciplined Boro side featuring some decent midfield moments on the part of Matt Crooks hogged plenty of possession but kept things fairly tight. Retaining their composure, Wilder’s players took no unnecessary attacking risks as Spurs, too, stayed patient and seemed content to play very much on the counterattack. They might have taken the lead on one such break but despite Lumley charging unwisely off his line and watching in horror as Doherty rounded him, the right wing-back ended up missing an open goal, shooting wide from an admittedly awkward angle. In the absence of much goalmouth action the subplot involving the quick, elusive Sessegnon and Boro’s right wing-back Isaiah Jones proved compelling. Going forward, Jones consistently looked the home player most capable of getting behind Conte’s backline and his sharp advances helped take the edge off the mood of slight impatience starting to permeate the cool Teesside air. It, albeit temporarily, evaporated as Duncan Watmore accelerated beyond three visiting defenders and played in Jones who promptly collapsed in close proximity to Sessegnon. The Riverside demanded a penalty but Darren England, the referee, was not fooled, swiftly dismissing Boro’s forlorn appeals. That incident seemed to bring out a certain indignation in Spurs and, shortly afterwards, Lumley did well to divert Eric Dier’s subtly curving free-kick behind. Kane thought he had volleyed his side ahead after connecting with a flick-on from the ensuing corner but, much to the Riverside’s collective delight, that effort was disallowed for an offside. By now it was clear that an unusually irritable-looking Kane was struggling to hit the imperious heights he reached at Leeds and it seemed thoroughly emblematic of his evening when he slipped while taking a dangerously placed free-kick before watching the ball roll harmlessly into the wall. Howson very nearly showed him how to do it, curling a dead ball of his own fractionally wide of Hugo Lloris’s goal. At this stage Conte was running through his full repertoire of sorrowful technical area expressions and, immediately after the unmarked Arsenal loanee Folarin Balogun, newly on for Watmore, shot off target when well placed, Tottenham’s manager made a double substitution. As Balogun doubtless regretted leaning back as he met Andraz Sporar’s fizzing pass, Emerson Royal and Steven Bergwijn replaced Doherty and Sessegnon. As extra time beckoned both sides switched formation to a back four but Boro finished the first 90 minutes stronger with Lloris saving from Jones and Crooks and Howson both also going close. Similar one-way traffic continued in extra time with Lloris denying Marcus Tavernier and Jones again while Howson miscued from a good position. Eventually Boro got their deserved break through. Coburn, an academy product from just down the road in Bedale, had just stepped off the bench when he met Crooks’ clever past and, holding off Cristian Romero, lashed a rising shot unerringly past Lloris and into the top corner from a tight angle.