Cardiff were 10th in the Second Division, two tiers below Leeds, and few were predicting a giant-killing at Ninian Park as the great John Charles, who played for both clubs, led the two teams out.
But Rio Ferdinand limped off, Alan Smith was sent off, and the animosity was such that O’Leary and Hammam almost came to post-match blows in the car park.
Leeds chairman Peter Ridsdale, who would later hold the same position at Cardiff, said the Yorkshire club’s eventual fall from grace could be charted from that eventful afternoon in the Welsh capital.
On Sunday, the two clubs will meet in the FA Cup again – reviving memories of Cardiff’s famous 2-1 victory over two decades ago and a day etched in Bluebirds’ folklore.
“If I played one more game that was the atmosphere I would want, it was volatile and electric,” said Legg, a former Wales international and a veteran of nearly 700 senior games for Birmingham, Cardiff, Peterborough and Swansea among others.
“I played for Wales and in a play-off final for Cardiff at the Millennium Stadium, but nothing ever came close to that.
“Some of the Leeds players didn’t go out wide that day. I won’t mention any names, but one or two of them told me: ‘They are nutters out there’.”
Leeds led early on through Mark Viduka, but Cardiff levelled quickly from Graham Kavanagh’s expertly taken free-kick.
Legg was then cast as the villain of the piece by Leeds as Smith was sent off just before half-time, referee Andy D’Urso adjudging that he had elbowed the full-back in the face.
“We’d had a few words in the tunnel before the game and people said I’d wound him up to the point that he reacted and got sent off,” said Legg.
“I was just close to him trying to get the ball and he tried to fend me off. I don’t think he intended it, but he caught me in the face.
“I didn’t think it was a sending off but I remember David O’Leary was on that side and he was saying all sorts to me. He wasn’t happy.”
With their one-man advantage, Cardiff sought a winner and a frenzied crowd reached boiling point when Hammam went walkabout around the perimeter of the pitch.
Hammam’s actions were designed to encourage home supporters, but missiles rained down on him from the terrace housing Leeds fans. Referee D’Urso was also struck by something thrown from the crowd.
Legg said: “I was taking a corner, I looked up and Sam was walking towards me on the side of the pitch. I thought: ‘Are you for real or what?’
“My problem was it was where the Leeds fans were and I got pelted by coins. They were trying to hit him and I got caught in it all.”
Just four minutes remained when Kavanagh swung over another corner and defender Scott Young pounced on the mayhem in the Leeds box to bury the decider.
Hammam was still on the side of the pitch when Cardiff fans invaded at the final whistle – earning them a £20,000 fine from the Football Association – and he had an altercation with O’Leary after the game.
Apparently the Lebanese businessman had reminded O’Leary of his pre-match quip that Leeds would “begin and end” their FA Cup campaign in Cardiff, which was also hosting the final at the Millennium Stadium.
Cardiff’s celebrations did not last long. Three weeks later, they fell at the fourth-round hurdle to Tranmere and manager Alan Cork left in February following a string of poor results.
For Leeds, it was the start of a long and painful journey. They would eventually finish fifth in the Premier League that season and miss out on Championship League qualification.
Leeds went into financial meltdown, forcing the sale of their best players and the club was playing in League One by 2007.
It took them 16 years to return to the top flight after relegation in 2004 and, although Cardiff and Leeds have since met in the second tier, Sunday’s cup tie will strike a chord for both sets of supporters.