The visitors booked their knockout place by topping their group, while the hosts only pipped Independiente Medellin to second place in theirs with a victory in the final round of games.
Match preview
Nacional booked their place in this year's Copa Libertadores group stage following another impressive domestic campaign, firstly triumphing over Liverpool in the Uruguayan Primera Division in the Torneo Intermedio final, as Yonathan Rodriguez hit the only goal of the game, before beating the same opposition to secure silverware in the Clausura Championship playoff, eventually running away with the tie in extra time following a 1-1 draw, as Luis Suarez netted his second goal of the match and Emmanuel Gigliotti notched up a brace in the additional 30 minutes.
They then entered the group in early April and enjoyed a fast start, firstly beating Metropolitanos 2-1 on their travels before triumphing by the same scoreline at home to Independiente Medellin, thanks to Fabian Noguera's 96th-minute winner after Gaston Pereiro's first-half opener was cancelled out 11 minutes from time.
Their knockout-stage hopes would then take a hit as a commendable 2-2 draw away at Internacional, courtesy of another decisive Noguera goal in injury time, was followed by a 2-1 defeat in the reverse fixture against Independiente Medellin, before again scoring late to force a draw against Internacional, with Bruno Damiani wrapping up a 1-1 draw with his leveller in the 89th minute.
That left the Tricolores third in the group heading into the final round of fixtures, but they were able to leapfrog Independiente Medellin and take a spot in the round-of-16 with a 1-0 triumph at home to Metropolitanos, thanks to Diego Polenta's goal in the 40th minute.
Following that triumph, Alvaro Gutierrez's side now head into the knockout stage on the back of a somewhat disappointing Uruguayan Primera Division Torneo Intermedio campaign in which they finished third in the table and missed out on the final, and they will be keen to get on the front foot in the two-legged contest on home turf.
They meet a Boca Juniors side who enjoyed a more comfortable ride through the group stage, after booking their spot in this year's Copa Libertadores by winning the Argentine Primera Division for the 35th time last season, amassing 52 points from their 27 outings.
The Argentinian giants began with a trip to Monagas and took a point from a goalless stalemate, before establishing their dominance in the group with a 2-1 beating of Deportivo Pereira in dramatic fashion as Luis Advincula netted an 89th-minute equaliser and Alan Varela scored the winner nine minutes into injury time, and a 2-0 triumph away at Colo Colo, courtesy of goals from Advincula and Sebastian Villa.
Their momentum was then halted by a 1-0 defeat in a trip to Deportivo Pereira, but Jorge Almiron's side quickly bounced back and guaranteed a place in the round of 16 with a 1-0 win to complete the double over Colo Colo, as Marcelo Weigandt hit the only goal of the match, before they sealed to spot and capped off the group campaign by beating Monagas 4-0 at La Bombonera, as Weigandt and Valentin Barco had them two goals to the good, despite being a man down, before Luis Vasquez netted a late brace.
Since that triumph at the end of June, the Azul y Oro have enjoyed a fine run of form domestically and head into Thursday's trip on the back of five straight victories across Primera Division and Copa Argentina action, most recently winning 2-0 away at Independiente, thanks to goals from Exequiel Zeballos and Nicolas Valentini, to cap off an admittedly disappointing league campaign in which they finished seventh.
Now with momentum back on their side under Almiron, Boca Juniors will look to come out on top in Uruguay to gain an advantage before welcoming Nacional to Buenos Aires for the second leg next week.
Nacional Copa Libertadores form:
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Nacional form (all competitions):
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Boca Juniors Copa Libertadores form:
D
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Boca Juniors form (all competitions):
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Team News
Nacional could field an unchanged starting XI from the one that finished off the group stage against Monagas at the end of June aside from the departing Federico Martinez, in Gutierrez's preferred 4-2-3-1 shape, with Diego Polenta and Fabian Noguera bound to continue their partnership at the heart of the back four.
Yonathan Rodriguez and Diego Rodriguez should again feature in front of them in the engine room, while Diego Zabala will lend support to the attack from in front of the midfield pairing.
The line will be led by Ignacio Ramirez, who has contributed 12 goals and three assists in 26 appearances in all competitions so far this season, with Gaston Pereiro and Franco Fagundez set to join him up front following Martinez's departure for Leon.
Although Boca Juniors may have looked to deploy an unchanged starting XI from their 4-0 thrashing over Monagas in their final Copa Libertadores group game in late June, they will be unable to call on centre-back Bruno Valdez, who will serve a suspension after being sent off in that game, meaning Jorge Vigal should again join Nicolas Valentini in the middle of the defence.
After starting up front in their victory over Independiente, Dario Benedetto could again lead the line, with further support from Palmeiras loanee Migue Merentiel, who has eight goals and three assists in all competitions so far this term.
Exequeil Zeballos will also hope to come into the front three after his goal off the bench last time out, with Valentin Barco having moved back to a full-back role last time out, while Cristian Medina and Alan Varela will again be crucial in the engine room.
Nacional possible starting lineup:
Rochet; Lozano, Polenta, Noguera, Candido; Y Rodriguez, D Rodriguez; Fagundez, Zabala, Pereiro; Ramirez
Boca Juniors possible starting lineup:
Romero; Weigandt, Vigal, Valentini, Barco; Medina, Varela, Fernandez; Merentiel, Benedetto, Zeballos