Hammers substitute Harewood celebrates his last-gasp winner
West Ham boss Alan Pardew and Arsenal counterpart Arsene Wenger were involved in an ugly touchline bust-up after Marlon Harewood's dramatic late winner.
Substitute Harewood sidefooted the ball in after fine build-up play from Teddy Sheringham and Matthew Etherington.
But in the celebrations that followed Wenger appeared to shove Pardew.
Tomas Rosicky and Robin van Persie - who seemed to be hit on the head by a coin thrown from the crowd in the first half - both went close for Arsenal.
Van Persie went to take a throw-in in front of the West Ham fans and after picking up the ball went down clutching his head.
He was okay to continue but the incident will undoubtedly feature in the referee Rob Styles' report.
It was just one incident in a pulsating game that came to life after the break.
Pardew dropped Sheringham from the side that beat Blackburn 2-1 last week and brought in Lee Bowyer and his side adopted a more physical approach to try to disrupt Arsenal's rhythm.
The plan paid off to a large extent but, despite the congested midfield, Arsenal's free-flowing football led to them creating some excellent openings.
Rosicky missed the best of these after 27 minutes.
The Gunners broke quickly and Thierry Henry's wonderful cushioned first-time pass fell invitingly for Rosicky but he fired wastefully wide.
And Hammers keeper Robert Green was forced to pull off a superb diving stop to keep out Van Persie's well-struck shot following Henry's neat header.
But West Ham had great chances of their own and could have been ahead after six minutes.
Quick thinking by Yossi Benayoun from a short corner freed up Etherington, whose driven shot deflected just wide of both the lunging Bobby Zamora and the far post.
And a dreadful clearance from Jens Lehmann resulted in Jonathan Spector finding space on the right but his driven cross was headed over at the near post by Benayoun.
West Ham's hopes of keeping a clean sheet were hit just before the interval when defender Ferdinand was forced out of the action with a damaged ankle.
But his replacement George McCartney played his part in keeping Henry quiet after the break and the Frenchman was restricted to a low, long-range effort that was comfortably saved by Green.
West Ham bravely switched to 4-4-2 just after the hour, bringing on the evergreen Sheringham and Harewood and taking off Bowyer and Zamora.
And both sides could have won the game in the closing stages.
The Gunners had strong shouts for a penalty waved away by ref Styles when Alexander Hleb appeared to be taken down by Spector.
At the other end a fantastic blocked clearance by Gael Clichy denied Sheringham the chance to grab his second goal in a week.
And Harewood raced through on goal after a fine through-ball from Sheringham but never looked confident and blasted the ball straight at the imposing figure of Lehmann.
Kolo Tore almost won the points with a fizzing shot from 30 yards, which beat Green but curled agonisingly wide.
But with seconds left Sheringham and Etherington combined brilliantly on the left flank and Etherington's teasing cross was calmly turned in by Harewood.
Pardew celebrated in true last-minute-winner style, leaping into the arms of his management team.
But Wenger took exception and the pair confronted each other, with the Arsenal boss appearing to push Pardew before they were pulled apart.
Wenger then appeared to refuse to shake Pardew's hand after the final whistle.
West Ham manager Alan Pardew:
"The performance of the players was the key. We looked to close them down and we were brave in the way we approached the game.
"Tactically it worked for us but it doesn't always.
"Football has a beauty of rewarding you when you least expect it. This was a big scalp."
West Ham: Green, Spector, Ferdinand (McCartney 44), Gabbidon, Konchesky, Benayoun, Bowyer (Sheringham 62), Mullins, Reo-Coker, Etherington, Zamora (Harewood 62).
Subs Not Used: Carroll, Tevez.
Booked: Spector, Benayoun, Harewood.
Goals: Harewood 89.
Arsenal: Lehmann, Hoyte (Flamini 76), Toure, Gallas, Clichy, Hleb (Eboue 71), Silva, Fabregas, Rosicky, Van Persie (Adebayor 61), Henry.
Subs Not Used: Almunia, Senderos.
Booked: Clichy, Van Persie.
Ref: R Styles (Hampshire).