Henrik Pedersen, the Dane whose shot cannoned off John Terry to beat Chelsea last week, stunned the new Premiership leaders seven days later.
Arsenal were hanging on to a 57th minute Robert Pires goal when Pedersen came on as a 74th minute substitute.
And then when the ball came to him in the 84th minute just inside the area, he fired in the goal that gave Wanderers a deserved share of the points.
It was the second time in successive away games that Arsenal had lost winning points in the dying minutes, Leicester grabbing an injury-time equaliser to deny them victory last time out.
This time Wanderers looked a good match for the leaders and were unlucky not to draw level within a minute of Pires' goal, Jay-Jay Okocha hitting a free-kick against the outside of a post.
Wanderers made the start that could and should have brought them a couple of goals in the opening quarter.
It was a confident opening with the midfield trio of Kevin Nolan, Okocha and Per Frandsen creating openings for both Kevin Davies and Youri Djorkeff.
In fact Davies had two attempts to beat Jens Lehmann but after his first attempt was blocked, he fired the second tamely at the keeper.
The best football of the opening quarter should have been crowned by the perfect finish.
However, after Okocha had played a delightful ball through to Frandsen, the Dane squared the ball inside for the on-rushing Djorkaeff only for the Frenchman to take his eye off the ball as he shot high over the bar.
Arsenal's attacking input had been spasmodic but Dennis Bergkamp was also guilty of a bad miss when he put the ball over from a good position.
On the half hour Nolan thought he had given Wanderers the lead when he turned away from his marker in the area and fired a shot that looked destined for the bottom corner, only for Lehmann to get the slightest touch on the ball and steer it away for a corner.
Arsenal managed to get their first shot on target at the start of the second half, Kolo Toure firing straight into the arms of the keeper.
That signalled the start of more threat from the Arsenal attack and it paid off when Bergkamp turned Ricardo Gardner and played the ball through to Thierry Henry.
His pass let in Freddie Ljungberg and when his shot was blocked it fell to Robert Pires who made no mistake, drilling the ball into the back of the net.
Wanderers almost made an immediate response when Sol Campbell gave away a free kick on the edge of the area but Okocha's curling shot clipped the outside of the post and rebounded clear with Lehmann beaten.
Djorkaeff then should have done better than fire wide with Davies well-positioned for a cross to the far post.
And when Frandsen looked to be chipping the ball into an empty net after the Arsenal defence had been tempted out by a corner, it was goal hero Pires who saw the danger and raced back to hook the ball clear.
Yet Wanderers were not to be denied and Pedersen came on to provide the vital touch, chesting down the lay-off from Davies before driving the ball home past Lehmann.