Queen of the South lost top spot in the Scottish Championship after slumping to a 5-0 home defeat to Morton.
They are replaced at the summit by Hibernian, who edged ahead on goal difference despite being held to a goalless draw at Raith Rovers following Marvin Bartley's first-half red card.
Falkirk are just a point behind in third place after claiming a 2-1 home victory over Dunfermline, while Dundee United also moved within striking distance thanks to a 2-0 win at bottom-of-the-table St Mirren which put them on 15 points.
Queen of the South's unbeaten start to the season came to a dramatic halt against Morton at Palmerston Park.
The leaders had conceded just four goals in their first eight league matches this term but were 3-0 behind inside 36 minutes following strikes from Ross Forbes, Jamie McDonagh and Gary Oliver.
After Forbes curled in the opener from just inside the area, McDonagh applied the finishing touch to a fine team move before Oliver, against his former club, found the bottom corner from the edge of the box.
Jai Quitongo hit the post at the start of the second half but went one better in the 64th minute, converting from close range, before Thomas O'Ware added a fifth from the penalty spot after Darren Brownlie fouled Forbes.
Hibs' third straight draw was enough to see them go top after a hard-fought stalemate against Raith at Stark's Park.
The visitors enjoyed the majority of possession early on as John McGinn's near-post header was cleared off the line before Fraser Fyvie went close as he sent Grant Holt's cross wide and Paul Hanlon then headed past the post.
Hibernian were reduced to 10 men seven minutes before the break as Bartley was shown a straight red card for a foul on Bobby Barr.
Jason Cummings fired wide from outside the box for Hibs, while Barr and Ross Callachan had chances blocked for Rovers before Kyle Benedictus's late header was kept out as Neil Lennon's side went home with a point.
St Mirren are still searching for their first win of the season after slipping to a 2-0 defeat to Dundee United at the Paisley 2021 Stadium.
Scott Fraser put the Terrors ahead in the 38th minute with his second goal of the season when a sharp interchange of passes saw Charlie Telfer play him in inside the penalty box and he drilled a left-footed shot beyond Jamie Langfield.
Gary Irvine then prevented Tony Andreu from doubling the advantage when he hacked the ball off the line.
But the on-loan Norwich striker was not to be denied and he wrapped up the points 16 minutes from time when he picked up a rebound in the penalty area to coolly slot home his seventh goal of the campaign.
The visitors finished the match with 10 men after Mark Durnan picked up two yellow cards in the final five minutes.
Craig Sibbald netted his third goal of the season as Falkirk secured a 2-1 derby victory over Dunfermline.
The midfielder opened the scoring in the 27th minute, lifting the ball over goalkeeper Sean Murdoch from John Baird's pass.
Sibbald missed the target on the stroke of half-time but the hosts did double their lead seven minutes after the interval as Myles Hippolyte cut inside and fired into the bottom corner.
Danny Rogers denied Farid El Alagui on two occasions but could not prevent the striker halving the deficit with 15 minutes remaining when he took the ball past the goalkeeper and slotted home.
Alan Forrest netted a hat-trick as Ayr cruised to a 3-0 win at Dumbarton, who have now gone seven games without a victory.
The striker opened the scoring in the second minute when he tapped in the rebound after Alan Martin parried Gary Harkins' shot.
Harkins fired over and then had a hand in the second goal in the 50th minute, squaring to Forrest who could not miss.
And Forrest completed his treble from the penalty spot after 62 minutes following Daniel Harvie's foul on Nicky Devlin in the area.