Ruthless Diego Costa sees off Middlesbrough and sends Chelsea top

Goodness knows how high on the scale Antonio Conte’s blood pressure might have registered had he nipped out at half-time and visited the NHS health bus in Middlesbrough’s carpark offering fans mini check-ups.

Watching the Italian’s technical-area histrionics it would have been easy to imagine his side were locked in a desperate relegation struggle rather than en route to going top of the Premier League courtesy of a sixth successive win.

Considering Chelsea have failed to concede a single goal during that sequence Conte generally has cause for serenity but on this occasion at least, his extreme agitation was at least partially justified by an ultra-determined, sporadically dangerous Middlesbrough.

No matter that Diego Costa’s winning volley from a badly defended corner reignited Teesside’s relegation worries, Adama Traoré’s pace and the midfield steel of Aitor Karanka’s two Adams, Clayton and Forshaw, left Chelsea looking slightly relieved to escape with all three points.

Karanka’s switch from his beloved, if sometimes rather rigid, 4‑2‑3‑1 formation to a much more flexible version of 4‑3‑3 helped a recent mini-renaissance featuring draws at Arsenal and Manchester City. It did not serve him too badly here either but Boro’s problem is that while they never look in danger of a thrashing they have won only twice all season and have a costly habit of making one unfortunate error per match.

The Teesside side started well with Gastón Ramírez troubling Victor Moses, the right wing-back in Conte’s transformative 3-4-3 system, and helping create an early chance which saw Álvaro Negredo – seeking his first goal since the season’s opening day – slice over from six yards. Unfortunately it proved to be the cue for a disappointing, less than mobile afternoon for the Spanish centre-forward which must have made Jordan Rhodes, once again sidelined, wonder precisely what he has to do to get a game.

If only Negredo had shown some of Ramírez’s ambition. Later, some woeful decision-making would let the Uruguayan down but, initially, he briefly looked capable of eclipsing even Eden Hazard – although it hardly helped the latter’s cause that he appeared to be singled out for some rough stuff by Karanka’s midfield.

After seeing Hazard clattered by a trio of early challenges, Jon Moss, the referee, finally booked Clayton for a particularly ruthless late lunge at the Belgian’s ankle.

If Hazard’s targeting cannot have been a shock, Conte looked affronted by Boro’s surprisingly effective amalgam of caution and aggression. Superbly compact as Chelsea advanced, with Clayton and Forshaw intelligence personified, Karanka’s players were not frightened to counterattack, utilising Traoré’s blistering, if ill-disciplined, pace to, at times, perturb the visiting back three.

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It meant, until Costa’s goal, Victor Valdés enjoyed a fairly peaceful first half. Admittedly the former Barcelona and Manchester United goalkeeper made one outstanding save when he diverted Pedro’s goalbound shot for a corner following exemplary approach work from Hazard and Moses, but he was largely well protected.

As half-time approached Costa had been largely anonymous, with Ben Gibson and Calum Chambers keeping him uncommonly quiet but then, in the 41st minute, a chance finally fell the centre-forward’s way and, typically, he was in the right place at the right time to seize it.

Hazard sent a corner looping high into the raw November air and no Boro player reacted properly. Valdés, who had just received lengthy treatment for an injury, should arguably have come for the ball as it looped up, while Gibson and Marten de Roon were among those who seemed to lose concentration. It left Costa free to meet a deflection, extend his left foot and volley his 10th goal of the season into the bottom corner from six yards.

As befits a world-class striker, he needed only a single opening to score but Costa had already caught the eye courtesy of some radically improved discipline. Hats off to Conte for eliminating the frequent am-dram theatrics which so annoyed opponents and officials when the striker served under José Mourinho.

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With Chelsea galvanised, the second half began with Moses and Hazard creating an opening for Marcos Alonso – guilty of an earlier bad miss – repelled by Valdés, with Chambers then doing well to block Pedro’s attempt to pounce on the rebound.

By now Moses was increasingly influential as he delighted in reminding everyone that Fábio da Silva was deputising for the injured George Friend at left-back and it was his first appearance of the season. Sensibly Karanka replaced Da Silva with Stewart Downing after an hour.

As icy rain poured down Clayton and De Roon began reasserting themselves against N’Golo Kanté and co, and Ramírez shot over the bar.

Chelsea’s minds seemed to be suddenly wandering and it took some extreme touchline gyrations from Conte – cutting an infinitely livelier, more agile figure than Negredo – until they refocused and Pedro’s shot hit the bar following fine work from David Luiz and Costa.

Deep into the second half Thibaut Courtois had still to make a significant save but when the call to arms eventually came Chelsea’s goalkeeper proved equal to it, saving Negredo’s shot superbly after Traoré’s pace caught his defence cold.

Middlesbrough are unlikely to be the last team similarly thwarted by Courtois, Costa and co.