Week 13 of the Copa Libertadores 2008 could prove to be an unlucky one for South American giants Boca Juniors and Sao Paulo, both of whom could find themselves exiting the continent's biggest club tournament over the next two days. With five places in the last 16 still up for grabs, FIFA.com looks ahead to the six games that will bring the curtain down on a typically unpredictable group phase.

Game of the week
Group 3:Boca Juniors-Maracaibo, Tuesday 22 April, 21.10 (local time)

The legendary Bombonera provides the setting for what promises to be highly dramatic clash between the holders and the already eliminated Maracaibo. Carlos Ischia's side lie third in the section on seven points, two behind Colo Colo and three off leaders Atlas, who meet in Santiago. A Mexican victory there will mean LosXeneizes just need to beat the Venezuelans to qualify. A draw would leave Boca needing to win by more than two goals, but should the Chileans prevail, the Buenos Aires heavyweights will need to rack up the goals to make sure of progressing. A nailbiting evening ensues.

The rest
Worryingly for the Argentinians, Atlas have yet to win on the road in the Libertadores this year. Nonetheless, Miguel Brindisi's men just need a draw to advance, while the Santiago side know a win will take them into the next round no matter what happens at the Bombonera.

Wednesday sees Nacional of Montevideo and Cienciano face off for the last remaining qualification ticket from Group 4, with Flamengo having already secured their place in the last 16. The odds appear to be stacked in the Uruguayan outfit's favour. As well as enjoying home advantage, Franco Navarro and Co are two points clear of the Peruvians and just require a point to become the only Charrúa side to make it to the latter stages. As for their guests, nothing less than a win will do.

Over at the Maracana, Fla will have their sights set on a goal feast against makeweights Coronel Bolognesi. A 5-0 win or better would see them pip Rio de Janeiro rivals Fluminense as the team with the best figures from the group phase and thus guarantee them home advantage in their future engagements in the knockout rounds.

The last of the eight pools to be decided is Group 7, where three teams are still battling it out for the two berths. Tied on eight points, Atletico Nacional and Sao Paulo lie first and second respectively and meet in a crunch encounter in Brazil. Oscar Quintabani's side have the edge on goal difference and will make sure of their place if they draw. Opposite number Muricy Ramalho will be hoping his side bag the three points so they do not have to rely on the outcome of Audax Italiano's visit to bottom club Sportivo Luqueno. A win for the Chileans in Paraguay will see them through regardless of events at the Morumbi.

Player to watch
Uruguayan striker Gustavo Byscayzacu has had a big hand in Colo Colo's strong showing in Group 3, and the Chileans will no doubt be looking to the 29-year-old to stay in the groove when they entertain Atlas. Byscayzacu already has five goals to his name and lies just two off the top of the Libertadores 2008 scoring charts. Can he add to that haul in Tuesday's big game and propel El Cacique into the knockout phase?

What they said
"I'm sure that when we play Maracaibo we will make up for all the chances we missed in our earlier games. I can't say how many we'll score, but I'm sure we'll get what we need to go through." Carlos Ischia is confident Boca Juniors can react in time to prevent their first group-phase elimination since 1994.

This week's fixtures:
Tuesday 22 April
Colo Colo (CHI) - Atlas (MEX)
Boca Juniors (ARG) - Maracaibo (VEN)

Wednesday 23 April
Flamengo (BRA) - Coronel Bolognesi (PER)
Nacional (URU) - Cienciano (PER)
Sportivo Luqueno (PAR) - Audax Italiano (CHI)
Sao Paulo (BRA) - Atletico Nacional (COL)

Teams already through: Cruzeiro (BRA), San Lorenzo (ARG), Estudiantes (ARG), Lanus (ARG), Flamengo (BRA), River Plate (ARG), America (MEX), Cucuta Deportivo (COL), Santos (BRA), Fluminense (BRA), LDU (ECU).