Rangers needed all three points to dislodge Nottingham Forest from the second tier's pole position ahead of the afternoon's fixtures and they were indebted to Johnson's close-range finish nine minutes after the interval.
Wanderers, meanwhile, have now failed to win any of their four opening Championship games but will highlight a tough start to the season which has seen them meet the R's, Forest and Reading already.
Prior to the game Bolton unveiled a statue of striker Nat Lofthouse, who scored over 250 times for them while registering 30 strikes in 33 appearances for England.
Lofthouse was a centre-forward who famously relished the physical side of the game, but even he might have winced at Richard Dunne's clumsy early challenge from behind on Jermaine Beckford which earned him a caution.
Dunne could get nowhere near to the ex-Leeds striker moments later, though, as Beckford raced away from him after picking up on Joey Barton's errant pass only to steer a good chance wide.
Barton, always the pantomime villain these days, joined Dunne in the referee's notebook after clashing with Lee Chung-yong and Rangers stopper Rob Green had to be alert to palm Jay Spearing's resulting free-kick over.
The visitors were creating chances too, Charlie Austin's long-range try deflecting narrowly over, but Wanderers nearly took the lead half an hour in.
Mohamed Kamara fashioned some space on the edge of the area and, urged by the crowd to go for goal, saw his effort pushed on to the post by Green as the first half ended in a stalemate.
All too often in the first period Austin and strike partner Johnson were running into similar areas, but both had a part to play when the deadlock was broken nine minutes after the interval.
Hoops captain Clint Hill marauded forward from left-back and, following a neat one-two with Austin, he drilled the ball across the face of goal for Johnson, who had just stayed onside to poke home into an unguarded net.
Wanderers boss Dougie Freedman sensed the need for fresh ideas and quickly introduced Craig Davies and Andre Moritz, the latter drilling wide from distance, before Rob Hall's arrival meant all three changes were made after just 72 minutes.
Hall in particularly gave the hosts a fresh injection of pace and when his through-ball found Davies ahead of him, Green displayed strong wrists to prevent his shot ending up in the bottom corner of the net.
But Green was not to be troubled again to leave Harry Redknapp's men sitting pretty at the top of the table.