The noise around an already eagerly-anticipated clash increased immeasurably when Boro accused Saints of snooping on training this week, leading to the south coast club being charged with a breach of EFL regulations.

Middlesbrough flew out the blocks fuelled by a sense of injustice, with Tommy Conway going agonisingly close on three occasions as Kim Hellberg’s hosts racked up 17 first-half shots at the Riverside Stadium.

Tonda Eckert’s distracted side looked like they could be on the receiving end of a 4-0 hiding like on January’s trip to Teesside, but Saints improved after the break, having taken the sting out of proceedings.

The visitors, unbeaten in the Championship since January, were far from their best but came close to snatching victory, with Taylor Harwood-Bellis seeing a six-yard header crash back off the crossbar.

The goalless first leg, and continuing brouhaha around ‘spygate’, sets things up fascinatingly for Tuesday’s St Mary’s shootout for a place at Wembley.

Binoculars and branches were among the props brought by Boro fans to a game that saw the team bus welcomed by thousands of supporters lining the streets.

That spectacular welcome left Conway “ready to run through a brick wall” and Hellberg’s team matched the intensity from the stands as they peppered the visitors throughout a one-sided first half.

David Strelec headed over from an early corner after Harwood-Bellis threw himself in front of a Riley McGree shot, with Saints needing to dig deep to keep the score level.

Morgan Whittaker whistled narrowly over from the edge of the box and McGree prodded across the face of goal.

Luke Ayling was allowed to burst forward and strike wide against uncharacteristically-ragged Saints, with a crucial James Bree block preventing Conway from opening the scoring from a deflected cross.

Further frustration soon followed for the forward. Middlesbrough broke after some foolish play by Cyle Larin and unmarshalled Conway slammed a low first-time strike off the post in the 34th minute.

Half-time could not come quick enough for Southampton, with Daniel Peretz just getting a hand to Conway’s close-range shot into the ground during a scramble at a corner.

Further opportunities followed before a break that Saints returned from with renewed purpose.

Ryan Manning fizzed across a tantalising cross that Ayling cut out and there was a collective intake of breath when Larin rose to meet a Tom Fellows cross with a close header.

Southampton had swung momentum and were starting to pose problems without asking serious questions, partly due to Leo Scienza’s unusually ineffective display.

Both sides made changes in a bid to force a winner, with Eckert’s team going closest in the 84th minute when Manning whipped over a free-kick and Harwood-Bellis’ close-range header rattled the crossbar.

Substitute Samuel Edozie made space to strike across the face of goal but there was to be no first-leg breakthrough as defiant Saints fans chanted “we’ll spy when we want”.