Arsenal triumphed at the Riverside tonight by beating Middlesbrough 2-1 to move back into sixth place, seven points behind Manchester City in fourth.

A first half goal from Alexis Sanchez and a Mesut Ozil strike with 19 minutes left, after Alvaro Negredo had equalised five minutes after the break saw Arsene Wenger’s men take all three points from the long trip to Teesside.

Yet the main talking point was Wenger making his biggest tactical change of the season by playing three at the back for the first time since 1997 - during a 3-1 victory over Derby County at the old Baseball Ground.

The move - prompted after the miserable 3-0 rout by Crystal Palace last Monday evening - saw the promising Rob Holding start his first league game since the 3-1 win at Watford back in August, to the left of Laurent Koscielny – who was back again after missing the last two games with an Achilles complaint. They were joined by Gabriel on the right.

The reason behind his thinking as he said pre-match was: “Recently we lost a lot of direct fights centrally. So it will get us a bit stronger in the air.”

Petr Cech also returned ahead of Emi Martinez with Nacho Monreal employed as a left wingback with Alex Oxlade-Chamberlain on the right.

In midfield Aaron Ramsey replaced Mohamed Elneny in the centre as the team shaped up in a 3-4-2-1 or 3-4-3 formation depending on whether they were in possession or not.

Olivier Giroud replaced Danny Welbeck - who had an injured toe - as Wenger made six changes in total.

Arsenal had picked up just seven points from their last eight games, while Boro have gained three points in the same period. The Teesiders hadn’t won a league game since 17 December – yet a win this evening would have lifted them to within three points of safety with a game in hand over 17th-placed Hull.

Boro were unbeaten in their last four league games against Arsenal at the Riverside – even if they conceded more Premier League goals against the Gunners than they have against any other side, 62 in 29 games.

It was all to play for – especially as Wenger’s men started the match in seventh place, 10 points off Manchester City in fourth place.

The Gunners started comfortably as the expected Boro onslaught failed to materialise. The change of formation looked to have given Oxlade-Chamberlain a new lease of life at right wing back as he regularly whipped balls in from the byline.

On 23 minutes his cross found Ramsey whose shot was deflected wide by Antonio Barragan. 11 minutes later Barragan on the six-yard line prevented a certain Sanchez goal again after a good cross from Oxlade-Chamberlain.

Granit Xhaka was flattened by Adam Clayton. The ball lay central at the edge of the ‘d’ as Alexis Sanchez whipped it up and over the wall to make it 1-0 on 42 minutes.

Sanchez’s goal was Arsenal’s 3000th away goal in English league football – only the second side to reach the milestone after Manchester United currently at 3226.

The Chilean’s goal meant only Thierry Henry with 12 scored more direct free-kick goals in the Premier League for Arsenal than Sanchez’s five.

However, five minutes into the second half a spirited Boro were level after Alvaro Negredo on loan from Valencia made it 1-1 after ghosting between the centre halves and getting on the end of a Stewart Downing cross as he stabbed home.

The goal meant Negredo has now scored five of Middlesbrough’s 13 home league goals this season with no other player Boro scoring more than two.

The home team nearly edged ahead but Cech blocked Ayala’s close range header 11 minutes later after first half substitute George Friend headed back into the box.

With 19 minutes remaining Mesut Ozil hit his 11th of the season to make it 2-1 to Arsenal against a spirited Boro after slamming the ball home from close range after a neat layoff from Ramsey.

With so much ground to make up Arsenal simply couldn’t afford to slip up tonight – and they didn’t.

But with season-defining semi-final against Manchester City at Wembley on Sunday the chase for the top four will be put on hold as both team’s fights for their only chance of silverware this season.

Whether Wenger will play three at the back under the Wembley arch is one question – the fact he took eight months of the season to react to Chelsea’s original successful decision to field a defensive trio as a backline is another matter entirely.

Middlesbrough:

Guzan, Barragan, Ayala, Gibson, Fabio (Friend 17), Clayton, De Roon, Leadbitter (booked 7), Ramirez (Traore 68), Downing, Negredo

Arsenal:

Cech, Gabriel, Koscielny, Holding, Oxlade-Chamberlain (booked 4), Ramsey, Xhaka, Monreal, Ozil (Bellerin 88), Alexis (Coquelin 88), Giroud

Referee: Anthony Taylor

Attendance: 31,298