Nicolas Colsaerts went from four ahead to four behind in a disappointing start to his second round at the Volvo Golf Champions in South Africa.
The 29 year old Belgian, whose only victory in nearly 200 European Tour starts came at last year’s Volvo China Open, had opened with a sparkling nine under par 64 in the 35-man winners-only event.
But on his return Colsaerts bogeyed the third, fourth, sixth and long ninth, where he blasted his drive into bushes, to turn in 40.
Home players Thomas Aiken and Branden Grace took over at the top, while Ryder Cup Captain José María Olazábal - at 596th in the Official World Golf Ranking the lowest-ranked player in the field - made his presence with a charge into joint third spot with five to play.
Open de España champion Aiken covered the front nine in 32, eight better than Colsaerts, to reach nine under, while Grace, who won the Joburg Open on Sunday to qualify, was one behind.
Open Champion Darren Clarke kept his hopes alive when a five under 68 lifted him from one over to four under and Masters Tournament champion Charl Schwartzel was alongside him after he shot 67.
Padraig Harrington, second on his own before he double-bogeyed the final hole of his first round, was in a tie for sixth spot on five under after 11 holes.
Grace rejoined Aiken with a birdie on the tenth, but Colsaerts's misery continued with a fifth dropped shot of the day two holes later.
Into third place came Slattery, who birdied the last for a superb 65, and also Harrington, who packed five birdies into eight holes from the seventh to be only one behind as well.
What made Slattery's day even better was that playing partner Goosen had shot 68 and their English amateur Mark Vandenberghe had also helped the two pros to win cars worth £25,000.
For the second day running Harrington finished with a double bogey seven - and having bogeyed the previous two this time he had fallen all the way back to four under.
That was eight behind Grace, who went three clear of the field with a hat-trick of birdies from the 14th.
