It always was wishful thinking that the occasion would pass off without any ugly incidents in the stands. They came so close. But just when it seemed that West Ham United were easing towards a largely peaceful 2-0 victory over Chelsea in the League Cup, fighting broke out between home and away fans behind Darren Randolph’s goal, transforming a magnificent night on the pitch for Slaven Bilic’s resurgent side into a PR disaster.

Stewards and police were forced to intervene, coins and bottles flew through the East End air and seats were thrown as rival supporters clashed on the concourse at the back of the lower tier of the Sir Trevor Brooking Stand for a couple of minutes. As the nonsense unravelled, Gary Cahill pulled one back for Chelsea at the death, but West Ham still went through to the last eight. Once again, however, there were serious questions to be asked of the level of security inside their new ground, which cracked under the strain of hosting a big match.

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Let’s avoid calling it a throwback to the 80s. That would be overly dramatic, while it should be pointed out that West Ham had worked hard with authorities to control the situation before the match. The actions of an idiotic minority marred the occasion, giving their fellow supporters an unwarranted bad name.

However the brawling that marred a rollocking match helped to explain why there were 11,000 empty seats inside a ground with a capacity of 57,000, with the prospect of hooliganism heightening the air of tension at the London Stadium.

After a dreadful start to the season, Bilic has revitalised West Ham in recent weeks and the manager was exasperated that the second question he was asked after the match was about crowd violence rather than his team’s excellence. It was a shame that the attention was dragged away from their third consecutive win. Such is life.

West Ham will be forced on the back foot again, with the Football Association likely to take a dim view of the scenes that everyone dreaded. Both clubs could face sanctions, while West Ham and the stadium organisers will have to reassess the organisation inside the ground. The ease with which supporters broke through the line of segregation caused deep concern. Stewards were outnumbered as fans converged on each other near one of the exits in the stand’s lower tier, creating a bottleneck. Sirens blared after the game. Families might well wonder if it is worth the hassle next time.

Organisational imperfections must be ironed out. With more than 5,000 Chelsea fans in attendance, only eight turnstiles were in operation and the away end was slow to fill up before kick-off, adding to the unease. Things calmed down. Inside the ground, the atmosphere was superb, a proper derby, feisty and thrillingly intense. Tempers flared again later on, though.

Facebook Twitter Pinterest West Ham United and Chelsea fans during the game. Photograph: Nick Potts/PA

Initially it was a relief to focus on the football when Cheikhou Kouyaté scored an early header and there was a sense that West Ham felt at home for the first time since leaving Upton Park. Edimilson Fernandes’s fine goal just after half-time secured a memorable victory.

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In the end, however, it was clear why West Ham could have done without this tie. Little has gone smoothly since moving to Stratford, from home fans fighting amongst themselves to issues over segregation inside and outside the ground.

The enmity between Chelsea and West Ham fans meant that this was the sternest test yet of policing and stewarding inside and outside the stadium. Supporters were advised to arrive early, many nearby pubs stopped serving alcohol an hour before the game and this was the first time that the streets outside were packed with police vans and officers on horseback, while plans were in place to keep home fans from the away end after the match.

When the inquest begins, though, West Ham should ask themselves why their first derby under lights did not take place in front of a sell-out crowd. Quite simply, it was the consequence of the shortcomings in security in previous matches. People will stay away if they do not feel safe. The price of a ticket should not come with the threat of a coin or seat landing on your head.