Celtic suffered their first defeat to St Johnstone at home since 1999 yesterday, after defender Dave MacKay's second-half effort secured an unlikely 1-0 victory.
Mackay, 30, struck on the hour-mark, volleying a deflected shot past Fraser Forster after the goalkeeper had parried a long-range strike by Jody Morris.
Celtic had tried, and failed, to find the net all afternoon. Their first opportunity came in the third minute when St Johnstone goalkeeper Peter Enckelman brought down Anthony Stokes in the area. Kris Commons, however, failed to convert the ensuing penalty, Enckelman diving to his right to repel the effort.
Another chance for the hosts came five minutes before the break, with Commons nearly atoning for his miss when his curling set-piece came off Enckelman's post. But their goal never came and Mackay's winner earned the Saints their first win of the season.
The result meant that rivals Rangers went top of the table after a 3-0 victory at Motherwell, bringing the hosts' unbeaten start to the campaign to an abrupt end.
Injury-hit Rangers went ahead after 20 minutes when Nikica Jelavic's goal-bound header from Steven Davis' corner came to Steven Naismith, the ball skimming off the striker's head and in.
Motherwell's Jamie Murphy bundled home to finish a move from a corner, but was penalised by referee Craig Thomson for using his arm to control the ball.
Rangers' second goal came on the stroke of half-time, when, on receiving Juanma Ortiz's pass, Kyle Lafferty drilled his shot in off the post. The hosts tried to reduce the deficit, with Chris Humphrey hitting the crossbar, but Rangers were pushing hard for a third and Steven Davis and Naismith also rattled the bar.
The third duly arrived with five minutes left, when midfielder Gregg Wylde beat Shaun Hutchinson for pace and fired home.