Windy conditions generally sent scores up -- as indicated by the 17-over-par 90 by Pablo Martin and that three other golfers failed to break 80 Saturday.
Even Grace, who had a four-stroke lead after the second round, had a 2-over 75. But Colsaerts, who was ahead by four strokes after the first round, turned in the second-best round of the day with a 4-under 69.
Colsaerts and Grace are at 10-under 209 after 54 holes and lead Retief Goosen, who shot 3-under 70 Saturday, and Charl Schwartzel, by one stroke. Schwartzel had an eagle, four birdies and one bogey for a 5-under 68, which was the best score Saturday.
Colsaerts salvaged a share of the lead with an eagle 3 at the 549-yard 18th. He'd opened play with a bogey at the first hole but dropped birdies at Nos. 4, 6 and 9 and was 2-under after 14 holes. He bogeyed the 15th but got back in front with a birdie at 16 and the 18th-hole eagle.
Grace was 3-over on the day before a birdie at the ninth hole. His second nine Saturday was an even-par 37 but included four birdies and double bogeys at Nos. 12 and 17.