The world number one and Race to Dubai winner has not competed in six weeks in order to prepare for an upcoming court case with his former management company.
However, McIlroy - a two-time major winner in 2014 - carded a bogey-free 66 in his first round at the Jumeirah Golf Estates in Dubai on Thursday and sits atop the leaderboard alongside Shane Lowry in the European Tour's season-ending event.
McIlroy had insisted he was fully motivated despite having already being crowned as the Race to Dubai victor and he showed his enthusiasm on Twitter ahead of his return to action.
"Just under 3 hours until I hit my first competitive golf shot in 6 weeks. To say I'm excited is an understatement," McIlroy posted.
And the Northern Irishman certainly seemed fired up as he collected four birdies in his opening five holes.
Nine straight pars followed before McIlroy picked up further shots at 15 and 16 to enhance his hopes of winning this tournament for a second time.
Lowry ensured that McIlroy did not take all the plaudits on day one, as he hit seven birdies and one bogey in a 66 of his own.
Scotland's Richie Ramsay signed for a bogey-free 67 to sit one shot off the pace, while Thorbjorn Olesen is also on five under – the only blot on his scorecard coming courtesy of a double-bogey six at the 16th.
Defending champion Henrik Stenson is in a share of fifth, the Swede mixing seven birdies with three dropped shots in his opening round.
Louis Oosthuizen and Edoardo Molinari are among a group of five players on three under par, while Justin Rose made five birdies in the last eight holes to recover from four over par to one under.