Wanderers again matched up well with Championship opposition before three goals in the final half-hour handed the Whites a first pre-season defeat.
A week on from beating West Bromwich Albion behind closed doors, Ian Evatt’s men continued their preparations with another serious test.
With a senior XI on for the first hour the Whites more than matched a Boro side which came up just four points short in their play-off push last season.
Wanderers had more of the play and the better opportunities in an excellent work-out at at Bishop Auckland’s Vest Construction Park.
But following a raft of substitutions – and not helped by a lengthy injury list - Michael Carrick’s side finished with the superior firepower and made it count to secure victory with two late strikes.
Wanderers were again missing a handful of their squad through injury, with midfielder Kyle Dempsey added to the list of those unavailable.
But those given a chance to further add to their fitness and state a case again did well against higher-ranked opposition a week ago from their opener against the Baggies.
Summer signing Klaidi Lolos was among those to show up well in an impressive first-half showing when the Whites looked the more advanced in their preparation.
Wanderers – with two central midfielders in George Thomason and Josh Sheehan and a three-man front line – moved the ball well and stretched the Teessiders, who were also playing their first open pre-season game after one run-out in Portugal.
The Whites had more of the ball in the opening half hour, although the best chance of that period arguably fell to Boro when Riley McGree got clear and then pulled the ball back for Izzy Jones, whose effort was well saved by Nathan Baxter.
Baxter had one more stop to make before the break, a straight-forward gather at his near post from Josh Coburn.
But it was the Whites who could well have been in front at half time. Their pressure on the ball and swift forays forward – often involving Josh Dacres-Cogley – brought a couple of openings for Lolos.
He looked as though he should have been awarded a penalty for a trip in the box before firing just wide. And when Dacres-Cogley clipped a lovely cross to the edge of the six-yard box, Victor Adeboyejo directed his header over the top.
Wanderers, starting with the same personnel, again threatened early in the second half once they had seen George McCormack fire an effort too high for the hosts.
Josh Sheehan steered an effort wide before the quick feet of Lolos again opened up the Boro defence to create an opening for Aaron Colllins.
Collins tested substitute Boro keeper Zach Hemming, who made it a double save when he got up to block the follow-up effort from Dacres-Cogley.
Mulitiple changes for the both sides then came on the hour and in the minutes that followed and as Wanderers were re-grouping, Boro took the lead through their top scorer of last season.
Latte Lath had scored 16 times in the Championship and wasn’t going to pass up the chance to get back in the groove when a through-ball was put into his path to slot home.
To manage the workload the Whites sent on a handful of their B Team youngsters but should have made it 1-1 with 20 minutes to go.
Dan Nlundulu showed all his strength to rob Hemming but then allowed the Boro keeper to recover and get enough on the striker’s attempted finish to divert the ball past the post.
And the Teessiders then made sure of the win when they made the most of that let-off to double their lead through Sonny Finch, who steered the ball in from close range after Latte Lath had headed down a corner.
With Wanderers’ best work behind them, Boro then added a late third when Scott Arfield fouled Dan Barlaser and summer signing Delano Burgzorg was able to settle into his new surroundings with a goal stroked home from the penalty spot.
Wanderers now head to Chorley on Tuesday night with a home double-header to come against Fiorentina and Stoke City as the countdown continues to the real thing in three weeks’ time.
Wanderers: Baxter (Coleman 60), Toal (Halford 68), Almeida Santos (Hayes-Green 68), Forrester (Johnston 60), Dacres-Cogley (Matheson 62), Sheehan (Arfield 60), Thomason (Morley 60), Conway (Inwood 62); Lolos (Bryan 68), Adeboyejo (Nlundulu 60), Collins (Eze 68).
Middlesbrough starting XI: Dieng (Hemming HT), Van Den Burg, Clarke, McCormack, Ayling, Azaz, McCabe, Morris, Coburn, Jones, McGree (Burgzog HT).
Middlesbrough substitutes used: Barlaser, Fry, Latte Lath, Gilbert, Dijkesteel, Howson, Engel, Finch.
Referee: Geoff Eltringham
Attendance: 1,560