Middlesbrough and Southampton could not be separated as a fascinating first leg of their Championship play-off somehow finished goalless.

After the build-up was spiced up by accusations of Saints spying on a Boro training session, the home side completely dominated the first half.

They had 17 shots to none from the visitors and came closest when Tommy Conway struck the inside of the post.

Saints improved after the break and could even have pinched victory late on when captain Taylor Harwood-Bellis thundered a header against the bar.

But with no goals scored, it is set up to be decided at St Mary's in the second leg on Tuesday (KO 20:00 BST).

Following Hull City's stalemate with Millwall on Friday, it is the second time in three seasons that both Championship play-off semi-finals have finished goalless in the first leg.

Championship play-offs rarely need any hype given the prize of Premier League football on offer for the winners.

But this tie was given added edge on Thursday when Middlesbrough accused Southampton of spying on a training session at their Rockliffe Park base, with the south-coast club subsequently charged by the EFL.

The dramatic episode added interest to what was already an intriguing match-up.

On the football side, when Middlesbrough hammered Southampton 4-0 at home in January, the gap between the sides was 13 points and 13 places.

Yet after 46 games, they were level on points, with Southampton one goal better off as they finished fourth and fifth respectively.

The Teessiders faltered badly in the run-in as they chased automatic promotion, while nobody matched Saints' tally of 47 points from the final 20 matches as they came flying up into a play-off spot.

Whether fired up by Southampton's alleged wrongdoing or not, Middlesbrough flew out of the traps with an intensity the visitors struggled to cope with.

Kim Hellberg's side registered nine shots in the first 30 minutes and should have scored with the 10th, but Conway's effort from five yards was brilliantly blocked by James Bree.

The Scotland forward was then released by Riley McGree as Saints carelessly lost the ball and Conway beat Daniel Peretz but struck the inside of the post.

The hat-trick of chances was completed when the ball dropped at Conway's feet following a corner, but his left-foot close-range attempt was scuffed, allowing Peretz to claw it away.

By half-time, Middlesbrough had enjoyed 76.1% of possession, while the visitors had not had a single shot in reply or even touched the ball in the opposition box.

Having been bossed in that first period, Southampton immediately improved in the second half and could have scored with their first attempt but Cyle Larin headed over after a lovely cross from Tom Fellows.

As a raft of substitutions disrupted the flow, it was Tonda Eckert's team who finished stronger and could have taken a lead back to Hampshire.

Harwood-Bellis, who was a rock at the other end, headed against the bar from Ryan Manning's free-kick, while substitute Samuel Edozie was inches wide with his shot after a quick counter-attack.

A goal did not arrive, but both sides will believe they are well capable of booking their place in the final at Wembley, which takes place on 23 May.

Middlesbrough boss Kim Hellberg told BBC Tees:

"The first half was the best I have seen on English soil since I arrived here – it was absolutely everything against such a good team.

"The second half was an even half where it was not as controlled, not as high quality maybe - they had a big chance at the end when they could have scored and that would have been very tough but it didn't go in like it might some weeks earlier.

"I couldn't believe my ears when I heard [about the spying claims]. I thought 'that cannot be right', but I tried to be focused on what we were going to do and go towards the game.

"You can watch all our games and you wouldn't find the structure we played in the first half in any.

"I don't like it, it's terrible - it has nothing to do with their supporters and their players, but it doesn't feel right and I don't like it."

Southampton boss Tonda Eckert told BBC Radio Solent:

"It was a proper game, the boys have been outstanding over 90 minutes and we take a lot of positives into Tuesday.

"Credit to Boro for a good first half, they spent a lot of energy in the first 45 minutes, you could see that Boro went all out.

"The game opened up in the second half a little bit more and we had two very big chances to win it at the end.

"The club made a statement [about the spying allegation] yesterday evening and that is all there is to say about it at the moment.

"The story draws attention but these games belong to the players, they are decided by the players and not the coaching staff and that's the important part.

"I've said all there is to say at the moment about that, we need to just focus because the game on Tuesday is going to need all of our energy."