The chant from the Arsenal fans was clear and it was directed at the press box. “You don’t know what you’re doing,” they sang. The target was not hunched over a laptop. This one was for Arsène Wenger, who had taken up residence among the folk he has variously described as snakes, sharks and philosophers over the years, as he served the second instalment of his three-game touchline ban.

The Arsenal manager had brought off Alexandre Lacazette in the 66th minute and the travelling support could not believe it. There were boos as the striker headed off and Alexis Sánchez came on. The latter had been the shock omission from the starting lineup, which formed the principle sub-plot of the evening.

Arsenal were in the throes of weathering a second-half storm in this Carabao Cup semi-final, first-leg. They simply could not get out as Chelsea probed for the opportunity to take charge. The frustration bubbled among the visiting fans. They had wanted to retain the outlet of Lacazette, however peripheral he had been.

Their team would hold firm and Wenger could enjoy a little succour in the face of what he calls the “circus” around his club. The jesters had been out after Sunday’s FA Cup exit at Nottingham Forest and it was a nervy ride as Chelsea made the running. But the home team could not find a way through.

They had 21 attempts on goal to Arsenal’s eight but only six were on target. David Ospina saved from Victor Moses and Álvaro Morata while he was helped out by his near post following another Moses shot. Cesc Fàbregas blew a free header, Andreas Christensen did likewise with two more and, after the 0-0 draw at Norwich City in the FA Cup on Saturday, it was no surprise to hear Antonio Conte bemoan his team’s profligacy.

That was not directed, he added, at Morata, who endured another difficult match. Conte did make the point that at least Chelsea had created chances. It was another occasion when the video assistant referee was in use and the technology was required to rule on Danny Welbeck’s 87th-minute challenge on Fàbregas inside the penalty area. Conte appeared to make the signal for VAR involvement – which, apparently, is not allowed – and there was a delay after the referee, Martin Atkinson, pulled back play for the decision, which was radioed into his earpiece. Happily, the right one was forthcoming. Welbeck had played the ball.

The Sánchez situation cast long shadows. When he is in the Arsenal squad, he starts. Not here. The club’s joint-leading scorer was on the bench. “You cannot explain every decision,” Wenger said. No one could explain this one without thinking of Manchester City’s January push to sign the forward.

Wenger was in the stands at Stamford Bridge last season – he was suspended for the league fixture – and he described it as an “uncomfortable” experience. He really slummed it this time. There were times when he banged his fist on the long blue ledge that serves as the desk, mainly when Eden Hazard or Morata went down. He kicked the chair in front of him – much to its occupant’s delight – and there were yells at plenty of decisions, both from Atkinson and Arsenal players. The emotions churned.

An animated Arsène Wenger with first team coach Jens Lehmann in the press box at Stamford Bridge. Photograph: John Sibley/Action Images via Reuters

The game was diverting without being gripping and Wenger cited the familiarity of these rivals as a cause for the impasse. This was their fourth meeting of the season – including the Community Shield.

Moses had already worked Ospina at his near post when he got a second bite at a chance inside the area on 28 minutes. He rattled the same post with a low shot, with Calum Chambers reacting quickly to clear. In first-half stoppage time, Fàbregas ought to have done better than to head at Ospina from César Azpilicueta’s floated ball.

Arsenal’s best moment came in the 22nd minute when Wilshere lofted a ball over the top for Lacazette but his finish, when well-placed, was wild while Alex Iwobi forced Thibaut Courtois into a save towards the end of the first-half. From the rebound, Moses was late into a challenge on Ainsley Maitland-Niles, who hurdled over it. Was there contact? VAR said no.

Chelsea turned up the heat after the break and it came to be a struggle for Arsenal to escape their half. The chances came. Christensen headed over; Morata felt the ball hit him in front of goal from a Fàbregas corner – he could not react in time – and the striker also extended Ospina.

Wilshere was forced off, having looked good in the first half, and he faces a familiar wait for a scan. He turned the ligaments in his ankle – the “good one,” according to Wenger – when he went to block a Danny Drinkwater shot. Wenger described it as a sprain.

Chelsea continued to push. Moses was denied by a fine block by Shkodran Mustafi while Christensen was off-target with another header from a corner, with Ospina out of position. The breakthrough would not come.