A capacity crowd saw Ayrshire rivals Ayr United and Kilmarnock battle out a blood and thunder Scottish Cup derby draw at Somerset Park.
Right from the start Ayr tried to use the conditions to their advantage by knocking the ball quickly and trying to put their premier league rivals under pressure. But it was the visitors who took the lead after nine minutes when Fernandez whipped the ball across the box from the right, Ayr keeper Stephen Grindlay got the faintest of touches and Pascali deflected home from close range.
However it didn't take long for Killie to get caught up in United's tactics and the Division Two side levelled after 14 minutes when Dean Keenan levelled with a diving header past Killie golakeeper Damien Rascle after Ryan Stevenson's left-wing cross was flicked on by David Gormley.
Ayr should have taken the lead moments later when Scott Walker headed wide after Chris Aitken's free kick found him at the back post.
Grindlay in the home goal had to look smart to tip Grant Murray's cross from the right over the bar after the wind forced it towards goal on the half-hour mark.
The wet and windy conditions were not for the faint hearted and Ayr were making the best of them.
The game settled down after a frenzied start and decent play from Gibson saw him beat two Ayr men, but his cross was caught in the wind and landed harmlessly on the roof of the net.
Gormley missed a couple of good opportunities to hand Ayr the advantage after the restart, his first effort blocked by the goalkeeper and his second nodded wide of the upright.
Kilmarnock forged ahead after 54 minutes after good work by Gibson on the left saw the ball centred to Bryson, who finished from just inside the area.
Ayr immediately tried to haul themselves back into the tie and Bryan Prunty was agonisingly close to meeting a Stevenson ball at the near post and poking home.
At the other end, Grindlay was called into action to pull off a superb double block, firstly denying Garry Hay's shot before keeping out the rebound from Wright.
Jim Jefferies' side squandered an opportunity to move further ahead with 15 minutes remaining when defender Mark Campbell's rash tackle on Hay led to a stonewall penalty for Kilmarnock.
Russell's effort from the spot lacked precision and was saved by Uniteds 'keeper Grindlay to keep Ayr in the hunt.
It was a crucial intervention as, with seconds remaining, substitute Williams volleyed home a Rascle punched clearance from the edge of the box to give United a sensational equaliser .
The striker's joy was such that he stripped to the waist and kissed referee Steve Conroy, who swiftly replied with a yellow card.
It was a magnificent team performance from the Hoest Men and the draw was the least they deserved.
United manager Brain Reid said "Financially, it's probably even better for the club that we got a replay, and maybe even for Kilmarnock as well.
"I think if we'd lost the game it would have been a bit of an injustice."
Sour grapes from the Kille manager when he said afterwards "Ayr got a massive lift. They pumped balls into the box and when they got corners these things were very difficult to defend. They're just hoping it falls for them, and fall for them it did."
Its a tribute to second division Ayr and a sad indictment on Killie that United were able to employ such tactics successfully against a premier league side.
There was no doubting that all forms of devilishly compelling derby life were to be found in this match. The enmity between the clubs runs deeper than many derby rivalries. Precisely why Somerset Park was packed.
The 9,280 punters inside the Capstan and flat-cap era ground lashed by a constant downpour came to vent their spleens as much as will their team to victory.
Games between the pair have been rationed in recent times, which could be a source of relief to Kilmarnock followers.
They were no doubt sick hearing all week how the last four meetings between the team had finished with Ayr victories. The likelihood of that run continuing was reduced no more than a smidgen when the Rugby Park men ended a 15-year wait for a goal against their rivals.
The replay will be on Tuesday 20 January at Rugby Park, Kilmarnock.