JOIN USSteelers had three players sent-off, including captain Hwang Jae-won and goalkeeper Shin Hwa-yong, in the second half, with goalscorer Denilson taking over in goal.
“We could have achieved more in this competition, but football gives us situations that are very bitter and this today was the case,” Pohang's Brazilian coach Sergio Farias told a news conference.
“The result doesn't reflect what we saw on the field and was made worse by the failures by the referee. I'm not talking about a conspiracy, but the failures of the referee,” he added, referring to Italian Roberto Rosetti.
Estudiantes coach Alejandro Sabella said: “Perhaps (Rosetti) whistled in favour of Estudiantes' superiority...but in general, he applied FIFA regulations to send off (the players) correctly.”
Benitez put Estudiantes ahead in first-half stoppage time when he slipped the offside trap to get behind Hwang at a free kick and steered the ball gently with his head inside the near post.
He increased Estudiantes' lead eight minutes into the second half before Brazilian striker Denilson pulled one back in the 71st minute when the Korean side were already down to 10 men, Hwang having been sent off for a second booking after a body check on wing Maxi Nunez.
In Saturday's final, South American champions Estudiantes will meet the winners of Wednesday's second semi-final between title favourites Barcelona and Atlante of Mexico.