The 18 teams on duty this week have varying objectives to achieve. For some the time has come to kick-start their campaigns, while others will be looking to take potentially decisive steps towards the knockout rounds. As the stakes start to mount in the Copa Libertadores 2008, FIFA.com looks ahead to nine games that should go some way to sorting out the genuine contenders from the makeweights.

Game of the week
Group 4: Nacional-Flamengo, Thursday 6 March, 19:00 (local time)

Having won the competition four times between them, Nacional and Flamengo are two of the best-supported clubs in South America. This Thursday sees the pair go head-to-head in a duel vital to the outcome of a pool that is proving hard to predict.

All four sides are still in the frame for a place in the last 16, with Fla standing top of the section on four points. El Bolso will leapfrog them if they prevail at their Parque Central stronghold, where they have gone unbeaten in their last five Libertadores matches, picking up 13 out of a possible 15 points last season.

The two group favourites go into their showdown buoyed by respective wins over Peruvian opposition in their previous games: while the Uruguayans secured a 1-0 win at Coronel Bolognesi, the Brazilians saw off Cienciano 2-1 in Rio de Janeiro.

The rest
Cruzeiro welcome Group 1 frontrunners Caracas FC to Belo Horizonte in another attractive clash. The Raposa are unbeaten after securing a point against San Lorenzo in Argentina and victory would see them swap places at the top with the Venezuelans, who have won two out of two so far. And with two-goal talisman Ronald Vargas suspended for Tuesday's tie, Caracas coach Noel Sanvicente will be delighted if his charges can come away unscathed.

That same day Santos entertain Group 6 adversaries Guadalajara in what promises to be an entertaining match between two attack-minded sides. Kicking off the day's action, however, is LDU Quito's home tie with Libertad, with both sides looking for their first win.

Brazil takes centre stage the following day. Carioca heavyweights Fluminense will be hoping to slip into the driving seat in Group 8 when they play host to Arsenal, who lifted the Copa Sudamericana 2007 without losing a single game on the road. Over in Group 7, meanwhile, Sao Paulo face a tricky assignment at the Morumbi against Audax Italiano. With last season's two meetings between the sides ending in draws, the 2005 champions should take nothing for granted.

Wednesday also sees a decisive showdown between Group 2 stragglers Danubio and Estudiantes in Montevideo. Although the two sides have only a point apiece to their name after two matches, the Uruguayans look to be in better shape following their creditable draw away to Deportivo Cuenca in Ecuador, where El Pincha fell to defeat just a week earlier.

Rounding off the midweek entertainment is the Group 7 encounter between Atletico Nacional and Sportivo Luqueno in Medellin, and the visit of Atlas to Copa Libertadores holders Boca Juniors in Group 3. Los Xeneizes tuned up for the tussle by taking over at the top of the Argentinian Clausura at the weekend, while the Rojinegros won again in Mexico to take their unbeaten streak to five games.

Player to watch
Cruzeiro striker Marcelo Moreno
Born in the Bolivian city of Santa Cruz de la Sierra to a Brazilian father and Bolivian mother, the 20-year-old forward is one of Cruzeiro's stand-out performers with three goals in the tournament to date. After turning out for Brazil at U-20 level, the marksman is now leading Bolivia's bid for a place at the 2010 FIFA World Cup South Africa™.

What they said
"We need to get in amongst them because a lot of sides sit back at the Bombonera and it doesn't work out. We need to try and find a way of catching Boca off guard." Atlas' Argentinian striker Bruno Marioni, who returns to his old club on Thursday.

This week's fixtures:
Tuesday 4 March
LDU Quito (ECU) - Libertad (PAR)
Cruzeiro (BRA) - Caracas FC (VEN)
Santos (BRA) - Guadalajara (MEX)

Wednesday 5 March
Danubio (URU) - Estudiantes (ARG)
Sao Paulo (BRA) - Audax Italiano (CHI)
Fluminense (BRA) - Arsenal (ARG)

Thursday 6 March
Nacional (URU) - Flamengo (BRA)
Boca Juniors (ARG) - Atlas (MEX)
Atletico Nacional (COL) - Sportivo Luqueno (ARG)