Boro's hopes of an FA Cup win at home to Marske United were scuppered by an injury-time strike from ex-Whitby man Matty Waters to earn a 1-1 draw.
James Walshaw had put Boro in front on 26 minutes and the hosts looked set to record a deserved win, but Waters' goal means the sides meet again on Tuesday night at Marske.
Boro almost made the worst possible start when good play from Curtis Round in the first minute down the left set up an unmarked Louis Johnson, but luckily the forward hit the post from five yards out.
This seemed to stir the home side into action, with Luke Lofts and Walshaw both spurning chances created by the lively Kian Spence.
On 13 minutes Danny Lowe put in a great block tackle to deny the visitors, and just two minutes later left-back Wayne Brooksby showed great skill on the left wing before whipping over a cross which evaded everyone.
Boro piled on the pressure as Spence chipped a shot narrowly over, and then fine play from skipper Michael Coulson led to a chance which Walshaw fired well over the bar.
Another corner led to Isaac Assenso's header sailing safely into the hands of United's former Whitby keeper Jack Norton, and then Coulson had a shot deflected wide from an acute angle.
From the resulting setpiece from Jordan Deacey, Walshaw volleyed the ball home from close range to put the home side deservedly ahead on 26 minutes.
United almost levelled immediately as Louis Johnson's volley was tipped wide by Tommy Taylor.
From the resulting corner former Boro defender Kevin Burgess headed past Taylor but Brooksby headed the ball clear to maintain Boro's lead.
Seven minutes before half-time superb play from Lofts and Walshaw set up Spence, whose shot was once again deflected wide by a United defender.
From the corner, Jack Johnson's close-range header was well-saved by Norton.
In injury-time, a hopeful Marske pass bobbled over Lowe and Pete Davidson's heads and set Louis Johnson free, but the forward stumbled and failed to get a shot away.
The second half was a rather scrappy affair, and there were few clear chances until the 69th minute when Assenso came close to making it 2-0, heading narrowly wide from a free-kick.
Brooksby, who was the pick of the Boro players, continued to shine in the second half at left-back, with some solid defensive work in addition to some fine crosses.
Nine minutes from time United had a strong shout for a penalty turned down when Andrew Stephenson looked to have been fouled in the area.
In the first of five minutes of injury-time Boro broke away and Coulson was clear on goal and his lobbed shot from the edge of the box looked to be sailing into the net but it bounced back from the inside of the post.
This proved to be a crucial moment as a couple of minutes later Marske worked an opening on their left flank and the ball was pulled back for ex-Whitby man Waters to fire into the net and make the final score 1-1.
Boro's woes were deepened as midfielder Jordan Deacey was fouled late on when breaking through, and suffered a broken collarbone in the process.
Boro: Taylor, Johnson, Brooksby, Davidson (Watson 46mins), Lowe, Assenso, Spence, Deacey, Walshaw (Fishley 83 mins), Coulson, Lofts (Annan 62 mins). Subs not used - Morgan, Thurston, Merris.
Marske: Norton, Martin, May, Garbutt (Blackford 71 mins), Burgess, O'Sullivan, Stephenson, Gott, Waters, Johnson, Round. Subs not used - Scott, Pritchard, Clark, Butterworth, Wilkinson.
Referee - Sam Packer.