They lie on 136, six under par at the Gary Player Country club 175 kilometres (110 miles) northwest of Johannesburg.
Bland shot a second successive 68 while Donald carded a 71 after an opening round 65 in the penultimate event of the DP World Tour season.
Malaysian Gavin Green, whose 65 was the lowest second-round score, and South African Branden Grace, who fired a 67, share second place one shot behind.
A one-time winner on the European circuit, Bland birdied four holes and did not drop a shot in a delayed second round after rain and lightning halted play on Friday.
Donald, the 2023 European Ryder Cup captain, needed a par four at the final hole to take the outright lead, but three putted.
The former world No. 1 birdied four holes and bogeyed three while seeking a first win in Europe since topping the 2012 BMW PGA Championship leaderboard.
Wayward tee shots cost first-round leader Ryan Fox from New Zealand dearly as he slumped to a 74 after starting with a 64.
The son of All Blacks legend Grant Fox had to play too many approach shots from the rough in a round that included four birdies, four bogeys and a double bogey.
Fox and Dane Rasmus Hojgaard, who produced a second straight 69, trail Bland and Donald by two strokes.
The third round will also be played on Saturday.