Wales finished the game with 10 men after Neil Taylor's mis-timed challenge earned him a red card, and Seamus Coleman what appears to be a broken leg.
Coleman was stretchered off with an oxygen mask, and rushed straight to hospital where he was stabilized for the night. Five more remain, but unfortunately they may have to be played without Seamus Coleman.
Taylor spent eight months out of the game after breaking his ankle in 2012 and midfielder Allen said the Aston Villa defender was devastated by the incident.
"Apparently it wasn't the best challenge in the world - I haven't seen it".
Republic of Ireland manager Martin O'Neill: "He's a fantastic player and character", said O'Neill on Sky Sports.
He said: "I'm not exactly sure, I must admit".
"It was a typical British derby game, there was needle all the way through it", Chris Coleman responded angrily to Irish reporters.
"But there are no complaints for me, saying the Irish boys are this, that or the other".
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The challenge came minutes after Gareth Bale had been shown a yellow card for a late challenge of his own and that booking will rule him out of the game against Serbia, a match that is crucial for the Welsh now. I don't want to see anyone sent off, but their tackles flying in everywhere, some from Ireland's boys, some from our boys. "We created some good chances and we were unlucky not to get a goal".
"We look forward to welcoming Seamus back to the Ireland team, following his recovery".
Wales moved onto seven points, the same as Austria, which defeated Moldova 2-0 at home.
"We've 11 points on the board".
"We've never really been in this situation, to be honest with you, where we've had to defend anything like this".
"Perhaps they might have thought they'd have won one of those [drawn] matches but the Georgia game, which they could easily have been beaten in, was never going to be easy".
Had Ireland snatched a late victor, as almost happened when James McClean's effort was deflected the wrong side of the post, Martin O'Neill's side would have remained two points clear at the top of the group.
Meanwhile, Serbia are starting to look like the group favourites that O'Neill believes they are and they take on Wales at the start of the summer.