While the frontrunners in Argentina, Brazil and Mexico continue their push for their national championships, this weekend the focus shifts to those sides hot on their heels in the title races. In China, meanwhile, the eagerly awaited start of the Super League has the nation gripped with football fever. As ever, FIFA.com is on hand to preview what should be a fascinating weekend's action.

Argentinian Clausura: Leaders out for more
The country's big two, River Plate and Boca Juniors, both face stiff challenges as they look to cement their two-point lead over their immediate pursuers. The Millonarios, who host their home game at Velez Sarsfield's stadium because of a sanction for crowd trouble, welcome an Arsenal side still reeling from their Copa Libertadores elimination in mid-week, while reigning continental champions Boca have an away-day assignment against lowly Olimpo in Bahia Blanca. At the other end of the table, in a match that could be decisive in the relegation battle, struggling Racing Club and San Martin de San Juan will meet behind closed doors after crowd disturbances by Racing supporters last weekend.

The big game
Estudiantes de La Plata-Velez Sarsfield
The pair lie third and fourth respectively just two points off the pace, but crucially with a game in hand on River and Boca. Saturday's showdown in La Plata is one not to be missed.

Player to watch
Leandro Gracian, who is emerging as a natural replacement for Juan Riquelme in the Boca Juniors midfield, was on the score sheet last week against Colon. Against Olimpo, in Bahia Blanca, he will be hoping to further his cause for a regular first-team slot.

Mexican Clausura: Can anyone stop Chivas?
Leaders and unbeaten in Group 3, Chivas of Guadalajara will be looking to keep their title bid on track with a trip to Necaxa, who have been inconsistent this season in the same group. On paper it looks like an away win, as the Rebaño Sagrado go into the match on a high after their 2-1 over Pachuca last weekend. Elsewhere, the meetings of Toluca-Monterrey and Santos-Tecos stand out, the latter pitting the leaders of Group 2 against the bottom-placed side in Group 1.

The big game
San Luis, the indefatigable pursuers of Chivas in Group 3, will have their work cut out against Group 1 leaders Jaguares in the pick of the games on matchday 12.

Player to watch: Omar Bravo, the Clausura's leading goalscorer on eight goals, will be a key man for Chivas against Necaxa as they look to stay out in front. The future looks bright indeed for Bravo, not least according to the vast majority (90 per cent) of visitors to the club's official website who predicted in a recent poll that he would finish as the league's top scorer this season.

BrazilianStateChampionships: Eagerly awaited clash between leaders
One of the standout fixtures from the latest matchday in Brazil has to be the meeting of the front-runners from Groups 1 and 2 of the Carioca Championship: Botafogo and Fluminense, the only sides still unbeaten in the league. Following proceedings closely and hoping to capitalise on any slip-ups will be Flamengo and Vasco Da Gama, the respective second-place sides in the two-group Taca Rio.

The big match
The latest meeting of age-old rivals Juventude and Gremio this Saturday looks the pick of the quarter-finals in the Gaucho (Rio Grande do Sul) Championship.

Players to watch
Wellington Paulista and Washington, the leading marksmen of Botafogo and Fluminense respectively, will continue their private goalscoring duel when their sides cross swords this weekend.

Chinese Super League: Let the games commence!
In China, this weekend sees the start of the 15th edition of the Super League in which 16 sides will battle it out for supremacy. Changchun Yatai, last season's surprise champions, kick off the defence of their title with a trip to Changsha Ginde in one of Sunday's key games. There will also be huge interest in the opening fixtures of Guoan, Dalian Shide, Shandong and Shenhua, the other four sides with serious ambitions of winning the title.

The big game
In Shanghai this Saturday, two former league champions, Shenhua and Shenzhen, will battle it out for their opening points of the season.

Player to watch
China PR striker Han Peng will be keen to pick up where he left off last season when he leads the line again for Shandong Luneng on their return to action.

Other leagues
Matchday 13 gets underway this weekend in the USA's MLS, which has seen its popularity continue to grow recently with the arrival of respected Argentinian Marcelo Gallardo (DC United) and the return of Guatemala's Carlos Pescadito Ruiz (LA Galaxy).

Further afield, in Iran, the Pro-League throws up a classic showdown between Esteqlal and Sepahan, who will be hoping to catch pace-setters Persepolis. With 41 points, the leaders can ill afford to ease up at this stage: Esteqlal lie in fourth on 37 points, while Sepahan, Asia's representative at the FIFA Club World Cup 2007, are in second place on 40.