Riot police were forced to intervene following West Ham's win over Anderlecht at London Stadium after sections of the home crowd were pelted with flares and seats by travelling fans.
Earlier in the evening, one fan was wrestled away by stewards after running onto the pitch during the fixture, ahead of the post-match disruption.
Anderlecht boss Felice Mazzu claimed to have not seen the flares, but a club spokesperson said after the match: "We don't tolerate this kind of behaviour from our fans and we apologise to West Ham."
Meanwhile, on the pitch, Jarrod Bowen found himself knocking on England's door so forcibly Gareth Southgate doesn't know whether it's a trick or treat.
But as West Ham cruised into the Europa Conference League knockout stage, Bowen's fifth goal of the season was a timely reminder to the Three Lions coach of his simmering form.
Of all the World Cup candidates lurking on the fringes of Southgate's squad for Qatar, none has a keener eye for goal from open play than the Hammers' versatile forward.
On a largely routine night in pie-and-mash country, Anderlecht were the latest to discover Bowen also has a left foot sweeter than a dessert trolley.
In truth, the Hammers' sixth win in seven games was a largely more low-key than bass clef, but they got the job done in the first half-hour.
Despite manager David Moyes' pre-match assurance that West Ham did not take their return to European orbit for granted, large pockets of empty seats – a rare sight at the Taxpayers Stadium - greeted his continental explorers.
The stayaways missed a DJ determined to deafen everyone before kick-off, two sets of fans chanting profanities at each other in English and hordes of visiting Belgians complaining about watery English beer – as well they might.
But the vulgar soundtrack was broken by Said Benrahma's free-kick, whipped over the wall and through the eye of the proverbial needle, after 14 minutes to put the Irons in front.
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Benrahma has blown hot and cold like a box set on Netflix for the Hammers, but the Algerian's second goal of the season was exquisite payback after he was fouled by Amadou Diawara to concede the free-kick 22 yards out.
West Ham's early optimism was checked by the loss of Angelo Ogbonna – who missed most of last season after cruciate knee ligament surgery – to injury, but the party mood resumed when Bowen found his range.
He controlled Emerson's low cross with the efficiency of a racketeer collecting protection money and beat Anderlecht keeper Hendrik van Crombrugge emphatically – minimal backlift but maximum damage – to make it 2-0.
Sebastiano Espositio's late penalty, after Ben Johnson was harshly penalised, left the Hammers six minutes of stoppage time to negotiate as Anderlecht's lunatic fringe ripped out seats and hurled flares to keep the East end constabulary occupied.
