Neil Thompson took temporary charge of Wednesday after Pulis' sacking was announced on the eve of the fixture.
The home side led at the break thanks to goals from Callum Paterson and Liam Shaw, but Duncan Watmore's early second-half strike made it a nervy ending period for the Owls.
The win was only Wednesdays' fourth home success in the whole of 2020.
Story of the match
The Owls started sprightly, having the game’s opening attempt on three minutes. Barry Bannan picked out the early run of Josh Windass from the free-kick, floating it into the path of the forward who flashed his volley across the face of goal and wide.
Moments later, Marvin Johnson almost provided Britt Assombalonga with the opening goal of the night. Johnson sidestepped a premature challenge from Moses Odubajo before drilling the ball towards the back post where Liam Palmer cleared the danger before Assombalonga could finish.
Assombalonga should have put Boro ahead on 18 minutes. Lewis Wing lifted the ball down the right-hand channel and into the path of Duncan Watmore. The winger held off pressure from Palmer before sending an inviting ball towards the back post, which was narrowly missed by Assombalonga on the slide.
Moments later, a poor pass from Windass allowed Assombalonga to turn and break at pace before he threaded the ball through to Johnson. The winger took the pass into his stride, however, Keiren Westwood closed down the angle to block Johnson’s angled effort.
Wednesday took the lead on the half-hour mark. Palmer orchestrated the move from halfway, chipping the ball over the shoulder of Paddy McNair and into the path of Paterson, who shifted the ball onto his left foot before guiding an effort past the outrushing Marcus Bettinelli.
The Owls doubled their lead just before half-time through academy graduate Shaw, who converted Bannan’s teasing ball into the six-yard area to score his first professional goal for his boyhood club.
Neil Warnock left the field visibly frustrated, and his half-time rollicking seemed to fire up Boro, who came out with a higher intensity.
Middlesbrough halved the deficit four minutes after the restart. A throw into the area was controlled in the area by Sam Morsy. The combative midfielder pulled the ball back into the path of Watmore who drilled the ball under Tom Lees’ challenge.
Boro were pelleting the Owls' box with balls into the area, but Wednesday often dealt with the pressure.
Just after the hour mark, Paterson forced Bettinelli into a smart save, pushing the Scotsman’s inventive flick beyond his near post.
Warnock’s side turned up the pressure even more, bringing on Chuba Akpom and Marcus Tavernier to bolster more bodies in the forward area.
The latter of the two missed a golden chance to level the scoring. Tavernier played a neat give-and-go with Watmore on the edge of the area before he dragged agonisingly wide of the far post.
Johnson then rifled a shot against the frame after making a darting run from the left, with 15 minutes remaining.
Boro’s pressure was relentless. This time it was Marcus Browne who missed the target, curling wide from just inside the area from Tavernier’s cut-back.
Chey Dunkley then denied Watmore just inside the area, making a well-timed tackle after the winger brought Marc Bola's pass under control.
Wednesday held on to move into 22nd place in the Championship table, narrowing the gap to two points from safety.
Wednesday find their attacking prowess once again
The sacking of Pulis seemed to let the Owls off their leash when going forward.
Caretaker boss Thompson allowed Wednesday to stray forward and attack in numbers, something that was missing during Pulis’ mundane spell.
They also maintained their resolute stature at the back after receiving a lot of pressure in the second half.
The freedom allowed Wednesday to express themselves, perhaps taking out their frustrations on the Boro side.
Ending 2020 in a brighter position
Boro started the year with Jonathan Woodgate and were struggling for a consistent run until they sacked their former defender after 38 games in charge, with the club just outside the bottom three on goal difference.
The experienced Warnock came in and helped keep the club in the division, winning four of the remaining eight fixtures in a congested relegation battle.
The 2020/21 season has seen an upturn in form for Warnock’s side, picking up 33 points from a possible 63, with Boro placing just outside the top six.
Warnock will be hoping that Middlesbrough can keep up this good form going into the new year as they push for the playoffs.
Man of the Match
The boyhood Owl was superb in central midfield for Sheffield Wednesday.
Shaw broke up play well, making two interceptions and two clearances. He also made a vital challenge in the area to deny Wing a goalscoring opportunity.
And to cap it all off, he bagged his maiden goal for the Owls before half-time to put his side two goals ahead.