Peter Hanson shot a 68 to finish alone in second place at 10-under-par 206. Fellow Swede Henrik Stenson followed at 8-under-par 208 while Englishman David Lynn was one shot further back at 7-under-par 209.
Donald, already a winner on the PGA Tour, has come back to the European Tour in search of precious Ryder Cup points and with one round to play at Barsebck Golf & Country Club. His quest might prove to be very fruitful.
'I think that I have shown some good from this year and if I can win here tomorrow then I will have a good shot for the Ryder Cup,' said Donald.
After a course-record 65 moved him into the outright lead after the second round, the Englishman played some spectacular golf early on Saturday to increase his advantage dramatically starting with a birdie at the opening hole.
Donald parred his next five holes before his approach to the par-4 seventh stopped within 3 feet of the hole for another birdie. He then hit his third shot to six feet for a birdie at the par-5 ninth to reach 13 under around the turn.
At the par-4 13th, Donald was fortunate enough to have his drive bounce back into the first cut and made the most of his second shot when he holed a 6-iron for an eagle.
Donald continued to make par down the stretch until his tee shots got away from him on the closing holes. He hit a bad drive and a bad second shot en route to a bogey at the 17th and hit another errant shot on his way to a bogey at the last.
'I am striking the ball as well as I have been all year,' he said. 'Overall I have had a good day today with a disappointing finish.'
While his lead could have been greater, the 26-year-old feels comfortable with a three-shot edge.
'I don't know exactly what happened at the end of the round,' said Donald. 'I think my concentration dipped and I got a bit out of synch at the end, but if I can go out and concentrate on playing the way I have been playing then I will be a hard man to catch.'
Hanson was four shots back to start the day, but made an early run, starting with a birdie at the par-4 third. Hanson then knocked his tee shot inside 15 feet for a birdie at the par-3 fourth and made it three straight with a birdie at the fifth.
The 26-year-old two-putted for a birdie at the par-5 12th to briefly pull within three of the lead, but gave that shot back with a bogey at the 15th. Hanson recovered with a birdie at the closing hole to earn a spot in the final group on Sunday.
Jesper Parnevik, a two-time champion of this event, posted a 71 to join Wilhelm Schauman, Steve O'Hara and Steve Webster at 6-under-par 210.
Paul McGinley, Carlos Rodiles, Charl Schwartzel, Simon Khan, Robert Coles and Christopher Hanell share ninth place at 5-under-par 211.