It was an area reserved for Crystal Palace supporters - some of whom, it has become clear, are not exactly model citizens - yet he had presumably been able to watch the match undisturbed, and apparently continued to do so.
It is hard to imagine that his presence would have been tolerated even five years ago. That is an indication of just how far football has come since the terrible days of the Seventies and Eighties, when to wear the away colours was to invite assault.
And yet it is not true to say the hooligans are now only on the pitch. An oft-made comment after the Cantona incident was: "If he had he done that at Millwall, he would never have got out alive." Since it was generally uttered by Crystal Palace fans, no friends of their south London rivals, one wondered just how far we have come.
Last week, a Millwall player echoed the thought in a Scottish newspaper. And on Saturday, when Millwall and Chelsea played out a scoreless draw at the New Den, it became apparent it had an element of truth.
Back in the bad old days, when I was writing on hooliganism, Lewisham police officers told me that opposing players had admitted they were terrified of playing at The Den. on winning a throw-in, they would chuck it anywhere rather than have to lurk on the touchline.
But Millwall now have a splendid new ground, and the club has made major efforts in combating racism and hooliganism. Unfortunately, it would seem the belief that people can be civilised by their surroundings is mistaken. New ground, same old hoolies.
Saturday's main outbreak of trouble was, admittedly, started by Chelsea fans. It is always difficult, despite a good vantage point, to follow the pattern of such incidents, but it would appear that having been upset by the denial of a strong penalty appeal in the match's closing minutes, Chelsea fans began arguing with stewards. Suddenly, the row gained momentum, and then there were several hundred Chelsea fans in the corner of the North stand pushing towards the police and Millwall fans.
A fold-up metal chair was thrown, striking a policeman on the back and head, then a few punches were traded and the atmosphere tensed. But with mounted police riding quickly into the fray, the Chelsea supporters were contained, although had they really wanted to go on the pitch, they could certainly have done so.
But in the adjacent East Stand, the wide gangways and aisles of its modern design had enabled a large crowd of Millwall supporters to gather quickly. By now the match had finished, but dispersing this mob was a slow and often violent process, in which tempers were lost on both sides as the police reclaimed the area seat by seat.
To the average, relatively law-abiding citizen, the most shocking aspect of this was the eagerness to fight the police. This is not to say policing at football grounds is always excellent, it is not - far too many people are arrested or ejected for simply singing. But on Saturday the police showed the benefit of experience, acting with alacrity and justification.
There were several other skirmishes, inside and out of the ground, yet to add to the sense of depression it transpired the police regarded the afternoon's events with "relief". "We would have liked no problems, but being realistic, it has not gone too badly," Chief Inspector Geoff Curtis admitted, as he reflected on a scoreline of five arrests, 15 ejections and three of his collegues in hospital.
Ironically, there was little in the match to raise such passions. Millwall, with the young left-winger Mark Kennedy outstanding, had much the better of the first half; Dimitri Kharin saving at the feet of Dave Mitchell, and Dennis Wise nodding Tony Witter's header off the line.
Chelsea, having stuck tighter to Kennedy, gradually took control of the second half. However, since they have beaten only Charlton at home in more than three months, they will not approach Wednesday week's replay with confidence - especially as Millwall have won at Nottingham Forest and Arsenal.
Overall, Mick McCarthy's young side looked much the better team, with Witter, rescued from QPR's reserves in mid-career, and Ben Thatcher excelling in central defence. Thatcher, who was only playing as Keith Stevens is suspended again, was full of promise. One tackle, on John Spencer, was followed by a move upfield so composed, one immediately wondered whether Alex Ferguson was keeping tabs on him.
But then he let the ball run too far, Wise nipped in, and Thatcher inexplicably kicked him up in the air. It was that sort of match. Not that Wise was always the injured party; he was booked for a late tackle he would have been sent off for had the referee been stricter, and twice he contemptuously kicked the ball away.
This was his first match back as captain; Glenn Hoddle, the Chelsea manager, having reinstated him because he feels Wise has "learned his lesson" after being stripped of it following his alleged assault on a taxi driver. Since the case is still being heard - it resumes next month - the decision seems premature.
But the abiding memory will be the problems off the pitch. It is the fear of this, rather than of being assaulted by a player, which keeps some fans away from football. Hooliganism has not been eradicated, merely suppressed.
But it was heartening to hear the Oldham fan on a better than average edition of Radio Five Live's Six-O-Six, complimenting Leeds fans on their behaviour as he sat in their midst on Saturday.
Millwall (4-4-2): Keller; Dawes, Witter, Thatcher, van Blerk; Beard, Roberts, Rae, Kennedy; Mitchell, Edwards. Substitutes not used: Savage, McCarthy, Carter (gk).
Chelsea (3-5-2): Kharin; Kjeldbjerg (Burley, 88), Sinclair, Johnsen; Clarke, Wise, Spackman, Peacock, Minto; Spencer, Stein. Substitutes not used: Furlong, Hitchcock (gk).
Referee: R Dilkes (Mossley).