Kewell, who had a quiet game throughout, out-paced Gillingham defender Barry Ashby, and the ball seemed to take a bobble on the muddy surface and Kewell only succeeded in blasting the chance over the bar, with the ball going halfway up the open terrace.
Leeds tried to play the game at their own pace, but had to quell an eager start by Gillingham, who knew that this was likely to be their best chance of causing an upset against a side wracked by disharmony at all levels.
Almost 1,300 Leeds fans helped to produce Gillingham's best crowd of the season of more than 11,000 and a banner before the game proclaimed: "Peter you are selling our souls".
The fans also chanted: "What the hell is going on" at chairman Peter Ridsdale, who was seated alongside England boss Sven Goran Eriksson, making one of his rare visits to a club outside the Premiership.
Chances were few and far between in the first half but Ashby took time out from his duties marking Kewell and Mark Viduka to plant two good chances wide of Paul Robinson's left-hand post.
Kewell and Alan Smith had chances that were saved by Brown, and Gillingham almost took the lead just before half time.
The Leeds defence was caught ball watching at the far post and Guy Ipoua nipped in at the far post and saw his effort come back off the post.
Leeds might have been grateful to go in at 0-0, but they soon made an important breakthrough almost five minutes into the second half.
Neil Barry adjudged that Paul Shaw had fouled Smith After a lot of deliberation Smith finally curled a delightful free kick around the Gillingham wall for his first goal in 13 games to end a lean run for the England man.
However, Kewell's bad miss stopped Leeds from taking a stranglehold on the game and the match really turned on the 80th minute dismissal of Viduka.
Viduka could hardly have got through the door of the Leeds dressing room by the time Gillingham equalised a minute later.
Roland Edge, who had by far his best game for the club, passed to Shaw and his cross was flicked on by Chris Hope for Mamady Sidibe to fire home.
Sidibe had a real old battle against the impressive Dominic Matteo and Lucas Radebe but took his goal well for his second in two games.
Gillingham kept battling away and Leeds were probably the happier to hear the final whistle that means a replay at Elland Road on Tuesday week.
Afterwards the main point of contention was Viduka's dismissal. Terry Venables said: "I've seen it once myself, and Mark says there was no real contact.
"It's disappointing but I think Hessenthaler made a lot of it. I knew what to expect coming here because Gillingham are a resolute, determined side but they've got some good players in their team like Sidibe and Shaw and I'm sure they will try to pass it more at Elland Road."
Hessenthaler said: "I'm not going to get into a war of words with Leeds about the sending off.
"As far as I'm concerned it was a high challenge, and I've got a mark to prove it and he should have been sent off.
"The referee was right there and saw what happened."