The 24-year-old secured the win though Abel Braga's side could have been beaten by a far greater number but for a series of fantastic saves from Diego Cavalieri
Fluminense were reduced to 10 men during the first half and rarely posed a threat in attack from then on. Boca assumed total control of the game but could only muster a single goal through Pablo Mouche early in the second half.
From the kick off Flu were looking to play the ball high into the box in the hope that Rafael Moura would win a header and cause havoc among the defence. Instead it was he who put the ball into the box in the 13th minute and following Wagner's header Jean poked the ball narrowly wide of the post.
Boca began to settle on the ball and after a shaky start they began to assert themselves on their opponents. The hosts could have gone ahead but a narrow save from Facundo Roncaglia by Diego Cavalieri preceded a Dario Cvitanich header that flew narrowly over the bar midway through the first half.
Boca's chances of taking a first-leg lead were improved in the 34th minute when Carlinhos was shown his second yellow card for a completely unnecessary handball.
Abel Braga was reluctant to make a subsequent substitution and it almost cost him in the 41st minute. Mouche broke through from the right and after beating two players his shot from an acute angle was held by Cavalieri.
Minutes later the Brazilian keeper again thwarted the Xeneize when he turned Rolando Schiavi's volley after a well-worked corner around the post. Soon after, the visitors were incensed when they were not awarded a penalty in stoppage time as Roncaglia blocked Anderson's goal-bound header with his arm.
Thiago Carleto was brought on to restore the Tricolor's defensive shape during the break but the deadlock was broken just seven minutes after the restart. Cvitanich threaded a beautifully shaped pass down the left-hand channel and Mouche shot across goal and nestled his effort in the bottom corner.
Flu had their backs to the wall as Boca dictated the tempo of the game and rarely got forward to test Agustin Orion. Juan Roman Riquelme took his time to pick out substitute Nicolas Blandi in the area but the young striker saw his shot on the spin blocked by the visitors' defence.
With 15 minutes remaining a dreadful attempt at the offside trap from a Boca free kick offered Schiavi a free shot on goal. Yet once again the centre-back could not get the better of Cavalieri who tipped his shot over the bar.
Julio Cesar Falcioni will have been pleased to have taken a win from the first-leg but would perhaps have liked a bigger margin to their victory. Fluminense must now win the return fixture at the Engenhao but their task will be made more difficult should Boca manage to score an away goal, giving the Argentines the upper hand.