Sonko struck from Stephen Hunt corners in each half as Reading, quicker and sharper than the visitors in every department, avenged an opening-day defeat by Plymouth the last time these sides met at the Madejski Stadium in August 2005.
That Plymouth win was the last time the Royals lost a Championship game at home and, in truth, that run never looked like ending.
Seven of Reading's starting line-up in this fixture featured in that game three years ago and the Championship clearly holds no fears for Steve Coppell's side after just two seasons of top-flight football.
Reading were ahead on 13 minutes, Sonko making the most of some generous marking to head home Hunt's corner and register the Royals' first league goal of the campaign.
Bobby Convey might have made it two but blazed high over the bar after Jimmy Kebe's low cross had sat up invitingly for him.
Plymouth rarely looked like levelling, though Jason Puncheon flashed a shot just wide two minutes after the restart.
But Reading responded to double their lead on 49 minutes with a carbon copy of their first goal.
Hunt's right-wing cross was again the source and Sonko's near-post header again punished some slack set-piece marking.
As Reading continued to dominate, Hunt almost added to his two assists with a goal, stretching to guide a header just wide from Kebe's cross, and Kevin Doyle nearly cashed in on more slack marking, only to be denied by former Reading keeper Graham Stack.
Convey again shot over after some neat control and the most spectacular effort on goal came from Leroy Lita, whose overhead effort flew just wide nine minutes from the end of a one-sided encounter.