Mesut Ozil grabbed a well-worked winner for Arsenal
The German international thrashed home a 71st-minute winner as Aaron Ramsey chested down an Alexis Sanchez cross to seal a first Premier League away win for more than three months.
It took the Gunners into sixth place, but still seven points behind fourth-placed Manchester City, with a game in hand on their FA Cup semi- final opponents.
Alvaro Negredo cancelled out Sanchez’s first-half freekick, but it was not enough for Middlesbrough, who remain without a league win since December, leaving them six points adrift of safety and heading for an immediate return to the Championship.
Wenger’s side took time to settle as the Gunners employed a back-three for the first time in almost 20 years, back in the days of Tony Adams, Steve Bould and Martin Keown.
A rather less imposing trio of Laurent Koscielny, Gabriel and Rob Holding manned a defensive line that was pressed back from the outset as Middlesbrough set out with purpose in search of a first league win of 2017.
Alexis Sanchez opened the scoring for the Gunners
Alex Oxlade-Chamberlain initially struggled to come to terms with the greater defensive responsibility he had to take on given the change in formation, and Gaston Ramirez took full advantage to provide a constant threat down the left on the South American’s return from injury .
Ramirez continued to be the hosts’ most potent attacking threat, and when Arsenal failed to properly clear a free-kick pumped into the box, from the Uruguayan’s lofted ball back into the area, Marten De Roon’s header found the net.
It was correctly ruled offside but was further evidence of Arsenal’s recent weakness at defensive set-pieces.
It took Wenger’s side almost half an hour to fashion their first decent opening as Ramsey latched onto an Oxlade-Chamberlain cross 15 yards out, only for his goalbound volley to be diverted to safety by Anton Barragan.
He came to the rescue of Brad Guzan, the goalkeeper standing in for Victor Valdes, after the Spaniard suffered a rib injury during training.
There was nothing the USA international could do as Alexis Sanchez put Arsenal ahead in stunning style three minutes before the interval.
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Arsenal line-up: The last time Arsene Wenger played three in defence Mon, April 17, 2017
Click to reveal the Arsenal line-up the last time they played three at the back (3-1 win over Derby, 1997)
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Arsenal line-up, the last time they played three in defence (3-1 v Derby, 1997)
Adam Clayton needlessly scythed down Granit Xhaka on the edge of the area, within perfect range for the Gunners’ setpiece specialist.
The Chilean did not disappoint, finding the top corner with a curling effort which sailed beyond Guzan .
Sanchez quickly went from hero to zero with an unwitting role in Boro’s leveller five minutes after the restart.
The South American’s ball was cut out by De Roon and swiftly funnelled out to Stewart Downing on the hosts’ right.
Alvaro Negredo got a rare goal for Middlesbrough
He was given far too much time and space to progress to the corner of the Gunners’ area before sending over an inviting cross, which Negredo volleyed home from close range as he brushed off a slumbering Laurent Koscielny.
It was only the 23rd league goal the division’s lowest scorers have mustered this season, one less than Everton’s leading Golden Boot contender Romelu Lukaku, to lift the roof off the Riverside and again see Arsenal’s defensive frailties again laid bare.
Olivier Giroud almost immediately restored the lead but the French forward’s effort was blocked bravely by Ben Gibson to prevent a goal.
As the game opened up, Daniel Ayala was denied a second for the Teessiders when Petr Cech saved well to deny the Spaniard’s diving header as Wenger’s men again looked vulnerable from another set-piece – before Ozil’s goal gave Wenger a lift.