Match ends, Middlesbrough 1, Arsenal 2.
Arsenal kept alive their hopes of finishing in the top four of the Premier League with a narrow victory at second-bottom Middlesbrough.
A dull opening was brought to life when Alexis Sanchez's superb free-kick gave Arsenal the lead just before the break.
Middlesbrough responded soon after the restart when Alvaro Negredo volleyed in Stewart Downing's pinpoint cross.
However, Mesut Ozil secured the much-needed three points for Arsenal with a first-time strike at the near post.
The win - only Arsenal's third in their past nine league games - moves the Gunners up to sixth, seven points behind fourth-place Manchester City and with a game in hand.
Middlesbrough remain deep in relegation trouble, six points from safety.
Wenger springs a three-man surprise
The Gunners have not lost five successive away games in the league since 1984 and manager Arsene Wenger took significant measures to avoid that happening against Boro by playing a three-man defence for the first time since 1997.
Rob Holding, Laurent Koscielny and Gabriel were the centre-backs at the Riverside Stadium but struggled with the change in system as Middlesbrough looked lively in the early stages but lacked the quality in the final third to exploit the gaps in Arsenal's defence.
"Yes, it is the first time in 20 years. That shows you that even at my age, you can change," Wenger said after the game when explaining his tactical switch.
"I felt it added a bit more stability on the long balls. We faced a direct game and we have been punished a bit on that. It gave the opponents more of the ball but against Crystal Palace we had 70% possession but lost."
Middlesbrough have scored the fewest amount of Premier League goals at home all season - just 12 prior to Arsenal's visit - and with the quality of Sanchez and Ozil in attack the visitors were always capable of snatching a lead. That proved to be the case when they scored from only their second shot on target just before the break, Sanchez expertly steering a free-kick over a packed wall and into the far corner.
Arsenal's lack of experience playing 3-4-3 was evident early in the second half when Downing charged away down an exposed right flank on the counter before providing the perfect ball for Negredo to poke in his ninth of the season.
The game opened up after that but Ozil's goal midway through the second half ensured Arsenal escaped with the points. It was a welcome win for under-pressure Wenger but not quite the sign of a return to form. Holding, Koscielny and Gabriel failed to make a single tackle in the first 60 minutes and stronger sides than Middlesbrough will not be as forgiving.
Sanchez smiling again
Sanchez has cut a frustrated figure at times this season, with reports suggesting he is keen to leave the Gunners in the summer.
However, his celebrations after Arsenal's goals on Monday did not look like those of an unhappy player.
He hugged and high-fived his team-mates and was seen smiling broadly at the final whistle, celebrating with the fans.
It is unlikely to be enough to convince Arsenal fans he will stay at the club, but it will no doubt have been pleasing for Wenger.
Is there hope for Middlesbrough?
Middlesbrough are the only side in English league football not to have won a league game during 2017 and that awful run of form has put them perilously close to an immediate return to the Championship.
Performances have improved since Steve Agnew replaced Aitor Karanka on a caretaker basis last month and this display was perhaps their best so far under the Englishman.
But wins are needed and needed quickly. Five wins and a draw from their final six games would take them to 40 points - generally perceived as the minimum to avoid relegation - but with games against Manchester City, Chelsea and Liverpool still to come they need to significantly improve in the final third to have a chance of pulling off an unlikely escape.
Man of the match - Alexis Sanchez
What they said
Middlesbrough caretaker boss Steve Agnew: "We are bitterly disappointed with the result but the players gave everything they had. We couldn't ask more of them.
"We played on the front foot, put them under pressure. I felt we might get the second goal after Negredo scored.
"The ball just wouldn't drop in the box for us. We put them under tremendous pressure."
Arsenal boss Arsene Wenger: "We responded well. I think it was not perfect but the commitment and focus was there. At 1-1 we found a response and managed to win.
"It was a big test, Middlesbrough gave everything. It's one of their last chances to stay in the league.
"It [the top four] is mathematically still alive. We knew we needed to win. Now we have a little break with the FA Cup and then we come back again to the league.
"We have to win every game to have a chance to get in the top four, starting tonight. I think it will make the team a bit more serene."
Sanchez to outdo Adebayor? The stats
- Arsenal picked up only their second win in their past nine away league games (D1 L6), though both victories came against teams currently in the relegation zone (Swansea were beaten 4-0 on 14 January).
- Alexis Sanchez has scored more away goals in the Premier League this season than any other player (13).
- Indeed, only Emmanuel Adebayor (14 in 2007-08) has scored more away goals in a single Premier League campaign for Arsenal than Sanchez this season.
- Middlesbrough are winless in 15 league games - their longest such run in the division.
- Only Thierry Henry (12) has scored more direct free-kick goals in the Premier League for Arsenal than Sanchez (five, level with Robin van Persie).
- Mesut Ozil has scored in two of his past three league games for Arsenal, the same number he'd scored in in his previous 16.
- Ozil also made four tackles, his joint-most in a Premier League game (last doing so against Man City in December 2015).
- Arsenal's opener was their 3,000th away goal in English league football (now 3,001) - the second side to reach that figure (Manchester United, 3226).
Middlesbrough continue their search for a first league win of the year on Saturday when they travel to Bournemouth (15:00 BST). Arsenal, meanwhile, now switch their focus to the FA Cup. They face Manchester City in the semi-final on Sunday (15:00).
- 2da SilvaSubstituted forFriendat 17'minutes
- 14de RoonSubstituted forGestedeat 79'minutesBooked at 82mins
- 7LeadbitterBooked at 7mins
- 21RamírezSubstituted forTraoréat 68'minutes
- 5GabrielBooked at 43mins
- 15Oxlade-ChamberlainBooked at 4mins
- 11ÖzilSubstituted forBellerínat 90'minutes
- 7SánchezSubstituted forCoquelinat 90'minutes
- Anthony Taylor
- Shots on Target
Second Half ends, Middlesbrough 1, Arsenal 2.
Nacho Monreal (Arsenal) wins a free kick in the defensive half.
Foul by Adama Traoré (Middlesbrough).
Attempt missed. Olivier Giroud (Arsenal) left footed shot from outside the box is close, but misses to the left. Assisted by Aaron Ramsey.
Attempt missed. Alex Oxlade-Chamberlain (Arsenal) right footed shot from the right side of the box is close, but misses to the right. Assisted by Granit Xhaka following a fast break.
Attempt saved. Alex Oxlade-Chamberlain (Arsenal) right footed shot from the right side of the six yard box is saved in the centre of the goal. Assisted by Héctor Bellerín.
Substitution, Arsenal. Héctor Bellerín replaces Mesut Özil.
Substitution, Arsenal. Francis Coquelin replaces Alexis Sánchez.
Attempt saved. Ben Gibson (Middlesbrough) left footed shot from very close range is saved in the centre of the goal.
Hand ball by Alexis Sánchez (Arsenal).
Offside, Middlesbrough. Daniel Ayala tries a through ball, but Rudy Gestede is caught offside.
Attempt saved. Daniel Ayala (Middlesbrough) header from the centre of the box is saved in the bottom right corner. Assisted by Adam Clayton with a cross.
Corner, Middlesbrough. Conceded by Rob Holding.
Rudy Gestede (Middlesbrough) is shown the yellow card for a bad foul.
Attempt missed. Olivier Giroud (Arsenal) left footed shot from the centre of the box is close, but misses the top left corner. Assisted by Alexis Sánchez.
Attempt saved. Álvaro Negredo (Middlesbrough) left footed shot from the centre of the box is saved in the bottom left corner. Assisted by Rudy Gestede.
Substitution, Middlesbrough. Rudy Gestede replaces Marten de Roon.
Foul by Nacho Monreal (Arsenal).
Adama Traoré (Middlesbrough) wins a free kick on the right wing.