Iain, who, like his late father, is a Hammers fan through and through, scored the winner for Stockport County in the fourth round replay of what was then the Coca Cola Cup after having notched a brace at the right end against Nottingham Forest in the previous round.
Next month, he returns as manager of Oldham Athletic hoping his side show no such generosity.
Even given West Ham's history against lower league sides in knockout competitions, the defeat at Stockport completed an exceptional double as, just a month later, Wrexham kicked the Hammers out of the FA Cup at Upton Park - though some would say the Swansea/ Northampton defeat double in 98/99 tops even that.
For Iain, whose spectacular bullet header following a corner was caused by him being somewhat caught out by the Edgeley Park floodlights, it was a case of turning the negative into a positive.
"Obviously the own goal and breaking my leg on the same day was a disappointing memory," he says, master of the understatement.
"But even that, when you look back on it, was a minor blip amongst all the good times - though it was that bad a day I try to forget it.
"My apologies for the horrendous own goal were received well at the time and these things are character building.
"I had to get over that and breaking my leg at the same time, and I think the West Ham fans understood my desire for the club when I played within four weeks of breaking it.
"I was never going to hide and all I can say is that I gave my all for West Ham - and I feel they appreciated it."
Iain did get some stick from the Hammers fans, especially in his second spell at the club, but Harry Redknapp was always willing to back him for his physical presence and work rate, even though he was not scoring regularly.
"I remember 'scoring' one against Wimbledon that was disallowed when I was on a run of 10 or 11 games without a goal," he says, "and I remember how good they were to me then.
"I have a lot of time for the West Ham fans and always felt they rewarded people who give 100%.
"There were some great times too; Harry took me back and I got 10 goals in the first season when we finished tenth in the league, and even though I wasn't there the full season I got runner up as player of the year.
"Even in my bad times when I couldn't score a goal the fans were good to me - even at the end when it wasn't going well they could see I was striving to get a goal.
"I scored against Notts. County at home to put us in the Premiership and playing against Manchester City to score two goals - all of these were pleasant moments that I have enjoyed.
"Those are the things I focus on and the bad things - it's documented that my own goal was the worst - you have to smile about now."
Iain, who recently got manager of the month for division two following a long sequence of wins for the Latics, is delighted to be bringing his side to Upton Park.
"It is a great, great, draw but we are fully aware of the gulf between us and what West Ham has become even since I left," he says.
"The club was the best I have ever been at as a pro for sure and my assistant David Cross - who is obviously much more of a legend than I was at West Ham - and I are very much looking forward to the game.
"Even Fitz Hall, who is with us and started as a kid at West Ham, can't wait, but it is a special time for me and David, having been there as players.
"To go there and get any type of result will be colossal, but we will try to entertain; I won't be looking to try and just shut up shop.
"We play to entertain, and we will try to do that even though there is a massive gap in class; we are trying to emulate West Ham but we know we are a long long way from it.
"It is going to be enormously difficult to contain the likes of Di Canio, Kanoute, Repka, David James, Joe Cole and players of that quality - and we are well aware we have a massive task on our hands.
"All we can do is go and enjoy it, that is what I have said to the lads; in the meantime there are a lot of league games to get through - but it is certainly a carrot."
"To have the fans' support at Upton Park was a lovely thing, and I know that Dave got nearly 100 goals for them in his time at the club so he had plenty of it.
"The East Enders and the West Ham fans are special people for me; they love their football and the quality of it - and demand to be entertained.
"Hopefully my lads will be able to do that when we play, but although it will be a good football spectacle we will have to defend for our lives.
"I am just looking forward to going back and renewing old acquaintances - and making it an unpleasant day for West Ham during the 90 minutes!"
Oldham knocked Derby out in the last round and last played West Ham in the competition in 1990.
A 6-0 defeat at Boundary Park - by which time most of the away fans had done the congo out of the ground in torrential rain - on February 14th led to the inevitable Valentine's Day Massacre headlines.
In the second leg, a 3-0 win restored a little pride - and there are those who were there that say if Julian Dicks' shot that hit the crossbar 10 minutes from time had gone in, West Ham could have gone on to grab two more for a sensational comeback.
But it is recent history that Iain is focusing on, and he says:
"Realistically we had a magnificent result at Derby and to be able to do that again - against a side that is a class apart from them - will be a story book tale.
"But win or lose hopefully people will say 'Iain Dowie is building a good little football club there', and that is what we are hoping to do.
"This is a fantastic tie against what I consider to be the best club in the country."
Iain has sympathy with Glenn Roeder's current plight and adds:
"I did my full badge with Glenn years ago, although I don't know him particularly well; he is obviously having trials and tribulations there, but he resurrected it last season after a difficult start.
"I have to say I think things will come good; he has got exceptional players, too many good ones, though I haven't seen enough of them week in week out to say what has gone wrong.
"All I can say is that I hope is that Glenn turns it round, and I am sure he will do that; if he can get back to clean sheets it will be important.
"But when it comes to the 90 minutes Glenn Roeder won't be worrying about me and I won't be worrying about Glenn Roeder.
"We both know that, and we have just got to get on with doing what is best for our respective clubs at the moment.
"West Ham is the first result I look for every week and I was bitterly disappointed that Birmingham beat them on Saturday.
"I know what Glenn is going through; it is a high pressure job, and you have to keep digging in and working as hard as you can."
Indeed, albeit in different circumstances, Iain sees a similarity between his position and that of Glenn, and he explains:
"I am probably like Glenn in a sense, making my way and a reputation in the game - I am very wet behind the ears but I have tried to do a lot of different things.
"We have made our club as professional as we can as Glenn has used John Green to help him do that.
"I have steered that myself in a way, and yes, if I am good enough it would be lovely to manage in the Premiership - and perhaps eventually to go back to West Ham, in whatever guise.
"But that is a long way off the road now and all I am going to do is concentrate on providing hopefully more success for Oldham Athletic and we will see where that leads after that..."