On a Wednesday night of high drama in Japan, Jeonbuk held the lead three times only for the hosts to claw their way back into the game before Hiroshi Kiyotake sensationally netted a late winner.
Having seen a brace from former Middlesbrough striker Lee Dong-gook and a single strike from Cho Sung-hwan give Jeonbuk a realistic chance of progressing to the last four, Choi was quick to declare that the tie is far from over.
"We eventually lost the game, but both teams played their best and fought for 90 minutes," he said.
"We lost concentration at the last minute and the result is disappointing. It would have been better if we could have drawn.
"But this is just the first-half of the game and we still have 90 minutes at home. We are strong at our home.
"We will work on what needs to be fixed for the return leg, which I think will be a different game."
Jeonbuk will now play host to Cerezo on September 27.