The Americans had fought back from 2-0 down at half-time to 2-2 when Donovan put a free-kick into the box and amid a tangle of bodies Maurice Edu applied the finish which looked to have completed an incredible turnaround.

But Malian referee Koman Coulibaly ruled it out and did not give any reason to the mystified Americans as they surrounded him at the time and again at the final whistle, with the match ending 2-2 to leave the group wide open.

Los Angeles Galaxy star Donovan said: "I'm assuming it was a foul somewhere, it couldn't have been offside. We asked many times who the foul was by but he wouldn't or couldn't explain it. I don't know what to think of the call, I didn't see a foul.

"To be honest I'm not sure how much English he speaks but when we asked in a non-confrontational manner why he had given the foul, he just ignored us."

Bradley was not given a satisfactory explanation either and felt if any infringement had been committed, it was by the defending Slovenians.

"In the midst of a game and everything that's going on it's rare that when a tough call is made that the referee will give you an answer.

"Sometimes, after the fact, you get an answer, and sometimes that's not the case either. Sometimes you are frustrated because you feel that situations have not been handled 100% correctly or fairly, but that's the way the game works and you move on."

Bradley added: "On the set-piece most of what took place was Slovenia players holding our players.

"A Slovenia player had his arms round Michael (Bradley, the coach's son), Michael tried to break clear and the foul was called. There might have been three fouls in the box, all of which were by Slovenia players."

Donovan rued his side's lacklustre start, with the excellent Valter Birsa allowed space to fire the European side ahead after 12 minutes and Zlatan Ljubijankic adding a second three minutes before the break after timing his run on goal well and finishing calmly.

The American said: "We started poorly and sat too deep which caused us problems, we had no choice but to push the game.

"We all spoke about believing that we could do it, my guess is there are not many teams in this tournament who could have done this, that is what the American spirit is all about. We knew we needed to score early in the second half."

Donovan obliged with a rocket of a shot from close range which beat Slovenia goalkeeper Samir Handanovic at his near post three minutes into the second period.

He recalled: "As I looked up my first thought was to pass the ball, at the end I decided to take a touch and aim high, aim at his head and I don't think he wanted to get hit from there.

"I felt relief because I knew at that point we had a chance to tie or even win."

Michael Bradley burst into the box with eight minutes to go to level it up after Jozy Altidore nodded down Donovan's high ball, and then came the Edu controversy.

Slovenia coach Matjaz Kek was proud of his side but admitted there was an "aftertaste" of sadness to have let slip a lead which would have booked his side's passage to the last 16.

"I am really proud of my squad but yes there is some aftertaste of expectations not having been met," he said.

"We were ahead of the US and we didn't overcome this pressure. There is pride and enthusiasm and maybe just a bit of disillusionment. This is a match we will learn from."

Slovenia next face England in Port Elizabeth on Wednesday but Kek refused to look ahead to the match at this stage.

"We are not considering our match against England at this point, my priority is to have my squad recovered, they have expended a lot of energy.

"We need to recover and then we will talk about England. It's very clear what we will be up against."