He attributed his return to form to not touching the clubs for almost two months during the winter break.
"It was time to have some family time with them for a couple of months and it was great," Donaldson said
"Come out for the season nice and fresh and you're reacting more to what you've turned up with, as opposed to slogging yourself to death over the winter."
China's Li Haotong, who finished one shot off the lead, carded a second successive 66, with South Africa's Branden Grace a shot further back following a 65.
The afternoon starters were unable to complete their second rounds before the play was halted for darkness at 1345 GMT, with four-times major winner McIlroy three off the lead with seven holes still to play.
After a delay of two hours and 50 minutes due to early morning fog, Donaldson claimed a birdie on the third and then made a six-footer on the eighth to make the turn at 33 and get to 12-under.
The 42-year-old Welshman dropped a shot on the 11th but a 15-foot putt on the 16th ensured he maintained the advantage at the top of the leaderboard.
Grace, who has a win and a runners-up finish in his last four starts, continued his impressive form as he carded seven birdies in a bogey-free effort.
Fellow South African Aiken Thomas turned in a 67 to finish 10-under alongside Spain's Miguel Angel Jimenez on fifth spot.
Englishman Matthew Southgate had a moment to savour when he made a hole-in-one with a nine iron from 154 yards on the seventh, and finished with an eight-under par total.
(Reporting by Hardik Vyas in Bengaluru; Editing by Matthew Mpoke Bigg)
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