Al Ain stunned Copa Libertadores winners River Plate 5-4 on penalties on Tuesday night after a lively 2-2 draw to clinch a place in the Club World Cup final and set up a potential showdown with Real Madrid in the United Arab Emirates.
River endured the humbling loss to the team from the UAE less than two weeks after thrilling its fans with a memorable win over fierce rivals Boca Juniors in the final of the Copa Libertadores.
Speaking after the match, coach Marcelo Gallardo said his team lacked the focus it needed for the match.
"The issue was our level of concentration against a rival that on paper was inferior," Gallardo said. "It was a dangerous match for us and when we let down our guard they were able to tie. [But] the party must continue because what we achieved was historic."
River entered the match as heavy favourites, but it quickly found themselves facing a more than worthy opponent than aniticipated.
Sweden international Marcus Berg flicked in a corner at the near post to give UAE champions Al Ain the lead on three minutes, but Rafael Santos Borre struck twice in quick succession to put the Milllonarios 2-1 ahead.
The Colombian forced in an equaliser from close range following a double save from Al Ain goalkeeper Khalid Eisa, and Santos Borre scored his second with a crisp finish from a Gonzalo 'Pity' Martínez assist.
However, Caio levelled for Al Ain on 51 minutes after a slick exchange with Japan defender Tsukasa Shiotani, before Atlanta United-bound Martínez slammed a penalty against the crossbar for River after Mohamed Ahmad brought down Milton Casco.
Al Ain converted all five of their spot-kicks in the shoot-out before River's veteran midfielder Enzo Pérez saw his effort saved by Eisa to send the hosts through to Saturday's final in Abu Dhabi.
"I hope not to be the Croatia of this World Cup because I hope to do better. They lost the final and I want to win it," said Al Ain's Croatian coach Zoran Mamic.
"Maybe it's something an Emirati must say. I've been in this country for a couple of years, but I think yes, that we are perhaps looking at the greatest success in football in this country. I'm proud to be part of this success. I hope the best is yet to come."
European champions Real Madrid, who are chasing a third successive Club World Cup crown, meet Asian champions Kashima Antlers of Japan in the second semi-final on Wednesday.
Earlier, African champions Esperance defeated Mexico's CD Guadalajara 6-5 on penalties to claim fifth place following a 1-1 draw in Al Ain.