So it turns out what Arsenal had been missing all this time has been an energetic deep-lying midfielder. Who knew? It was entirely fitting that it should be Lucas Torreira who rounded off their 4-2 victory in the north London derby on Sunday; he had been the key player in the game, not just for what he did with the ball, and without it, but because of what he embodies.

In the days of the debilitating niceness, Arsenal would probably not have come back from conceding two goals in quick succession just after the half-hour. Late-period Arsène Wenger would have bemoaned his luck, made arch comments about the disputed penalty, and everybody would have wondered just how Arsenal could end up losing so disappointingly having started so well.

Arsenal’s Aubameyang seizes moment with all-action display against Spurs Read more

Nor, you suspect, would Wenger have made the decisive tactical switch Unai Emery did after 71 minutes, bringing Mattéo Guendouzi on for Shkodran Mustafi and changing from 3-4-2-1 to 4-3-3 to combat Tottenham’s switch from 4-3-3 to 3-4-2-1 a few minutes earlier. Tottenham had started the game with a midfield diamond before adjusting their shape at half-time as it became apparent that the narrowness of their midfield was not merely not overwhelming the lesser numbers of a Torreira-fuelled Arsenal in the centre, but was opening the flanks to the home full-backs, Sead Kolasinac in particular. This was a game of big, bold tactical changes and it was Emery who came out on top.

But Torreira had a huge role in helping him to do that, adept playing just in front of the back four as part of the 3-4-2-1, allowing Granit Xhaka to operate as a more creative player alongside him, and just as effective pushing higher after the switch – which was, of course, what allowed him to make the run into the box that brought the fourth goal.

His impact on the side has been extraordinary. In the 965 minutes he has played, Arsenal have scored 28 and conceded 11. In the 295 he has not, they have scored four and conceded nine. Arsenal are yet to lose a game Torreira has started.

The Fiver: sign up and get our daily football email.

He’s not just a ball-winner, though: his pass completion rate is at almost 90%. In that sense, although he developed at Institución Atlética 18 de Julio (whose badge he wears tattooed on his calf) rather than a national academy, Torreira represents Óscar Tabárez’s ideal of the new Uruguayan player. Tabárez, who has effectively run Uruguayan football since 2006, spent much of the summer telling anybody who would listen that when his country beat Brazil to win the 1950 World Cup they committed only 11 fouls. This, he insisted, was proof that Uruguay’s historical style was tough but not brutal, that it was possible to be committed without being dirty.

He has worked over the past 12 years to re-establish technical ability rather than aggression as the defining feature of a Uruguayan midfielder, which is why the national team is now staffed not by the likes of Egidio Arévalo Rios and Diego Pérez but by Rodrigo Bentancur, Matías Vecino and Torreira.

The most disappointing thing about Torreira, perhaps, is the song with which Arsenal fans salute him. Although in repackaging an old favourite about Patrick Vieira, his role in the team is acknowledged, the line “he’s only five foot five”. (Given Torreira comes from Fray Bentos, fabled for its meat packing plant, and last year bought a butcher’s shop for his family you wonder if it’s too late to change that line to “He likes a corned-beef pie”).

Facebook Twitter Pinterest Lucas Torreira battles for possession with Dele Alli. Photograph: Julian Finney/Getty Images

He is, though, undeniably short for a Premier League player. A photograph from the first half on Sunday that showed him challenging Dele Alli (above), thanks to a trick of perspective, made him look like a Lilliputian surprising Gulliver by thrusting an arm across his chest and whipping the ball off his toes.

Sunday felt like a major moment for Arsenal, a day on which they flirted with carelessness and rejected it, in which their manager came out on top in a major tactical battle. But most significant perhaps is the proof that, at last, they have solved the problem at the back of midfield. The answer was not Mikel Arteta, or Francis Coquelin, or Mohamed Elneny, or Granit Xhaka, but it looks as though it may be Torreira. A decade after Gilberto Silva left the club, he has at last been replaced.