Lucas Alario netted the only goal of the game to help River Plate to the final of the Club World Cup at the expense of Sanfrecce Hiroshima in Osaka on Wednesday.
The 23-year-old broke the deadlock after 72 minutes following some unconvincing goalkeeping from Takuto Hayashi to set up a meeting with Barcelona or Guangzhou Evergrande Taobao in Sunday's showpiece.
Sanfrecce carved out the better chances in the opening 45 minutes, with Yusuke Minagawa in particular causing River all sorts of problems.
River keeper Marcelo Barovero proved to be too much of an obstacle, though, while he also denied Yusuke Chajima.
Marcelo Gallardo's River were the better side after the interval and were eventually rewarded when Alario broke the deadlock with a header, after Rodrigo Mora had previously missed an excellent chance to open the scoring.
Sanfrecce were unable to force an equaliser in the closing stages, and the J.League champions will now face the loser of Barca's clash with Guangzhou in the third/fourth-place play-off on Sunday.
River were the first team to threaten after a cautious start from both sides, with Leonardo Ponzio trying his luck from long range after 20 minutes, but Hayashi was not overly troubled and comfortably gathered the ball.
Matias Kranevitter was next to unleash a powerful shot from outside the area, only to blast his attempt high and wide.
Sanfrecce then slowly grew into the game and got a fine chance to open the scoring in the 26th minute. Minagawa took advantage of some poor defending from Eder Balanta, but Barovero showed his class with a fine save to deny the forward.
The Japanese side looked dangerous again shortly after when Chajima cut inside from the left before firing in a powerful right-footed shot from inside the area, but Barovero again came to the rescue for Gallardo's men.
Sanfrecce continued to cause River problems with their quick counter-attacks and Minagawa came close to breaking the deadlock shortly before the interval with a volley from the edge of the box, yet Barovero made his third excellent save of the half to keep it scoreless.
River made a fine start to the second half and should have gone a goal up within minutes of the restart, only for Mora to blast his shot over the bar from five yards out after a low cross from the left.
Gallardo's men did eventually get the opener with 18 minutes left after some poor work from Hayashi. The Sanfrecce keepr was beaten in the air by Jonathan Maidana after a free-kick from the right and Alario had no trouble heading home into the empty net.
Sanfrecce then failed to create any chances of note to level the scoring, as River progressed to Sunday's final.
