An exquisite goal by Colombian Leonardo Castro helped Mamelodi Sundowns triumph this weekend and stretch a South African Premiership lead to six points with five rounds left.

Castro and Zimbabwean Khama Billiat struck within four first-half minutes to earn the record six-time champions a 2-0 home victory over relegation-threatened Jomo Cosmos in Pretoria.

Second-place Wits unexpectedly dropped two home points when held 0-0 by mid-table Free State Stars, who played most of the second half in Johannesburg a man short.

Sundowns have 58 points and Wits 52 in a two-club race to the May 21 finish line and the contenders square off in Johannesburg in the penultimate round.

Castro has proved a good investment since joining Sundowns this season from Bolivian side Universitario de Sucre after spells with Colombian and Peruvian cubs.

The 26-year-old striker from Bogota has scored nine Premiership goals -- four less than Zambia-born charts-topper Collins Mbesuma from Mpumalanga Black Aces.

And arguably the best of those nine goals came against Cosmos after 31 minutes at Lucas 'Masterpieces' Moripe Stadium in Pretoria township Atteridgeville.

A deep cross from Billiat found Castro unmarked at the far post and he instinctively chipped the ball over goalkeeper Thabo Modiba and into the net.

The brilliant goal compensated the Colombian for not converting two scoring chances within six minutes of the kick-off.

Billiat doubled the lead when he latched on to a defence-splitting pass by Hlompho Kekana, got past a defender and beat Modiba from close range.

Conscious of conserving energy ahead of a midweek CAF Champions League qualifier against V Club of the Democratic Republic of Congo, Sundowns were content to defend the lead.

Wits coach Gavin Hunt once again lamented missing chances after Wits failed to score against a Stars side reduced to 10 men by an early second half red card.

"We should have won by a cricket score," said the winner of three consecutive Premiership titles when coach of SuperSport United.

"The play acting of Stars' goalkeeper did not help as the constant stoppages for treatment of his injuries upset our rhythm."

The winless run in all competitions of outgoing champions Kaizer Chiefs extended to eight matches after drawing 0-0 with Ajax Cape Town in a largely dour Soweto duel.

At the bottom, Maritzburg United appear doomed to automatic relegation after losing 2-0 to Black Aces, a second successive home defeat for the season-long strugglers.

Pretoria University drew 1-1 at Bloemfontein Celtic to move one point above second-last Cosmos and their May 1 clash is sure to have a major say in who is forced into play-offs.