Rangers maintained their perfect start to the new season with a 2-1 victory over previously unbeaten Kilmarnock, while Celtic hammered Hearts 5-0 to keep the pressure on at the top.
Hibernian came from behind to draw 3-3 with Aberdeen, Gretna's troubles continued with a 2-1 defeat at home to Motherwell and Dundee United coasted to a 3-0 win over Inverness Caledonian Thistle.
Hearts remain without a win this season after suffering a heavy defeat against the defending SPL champions. A Christophe Berra own goal set Celtic on their way after nine minutes before Massimo Donati made it 2-0 in the 22nd minute. Scott Brown added a third after 61 minutes and a Jan Veneggor Hesselink penalty (63) and Shunsuke Nakamura flick (79) completed the rout.
Billy Mehmet grabbed the crucial goal for St Mirren in the 90th minute after a tight game at The Falkirk Stadium.
Chris Porter secured the three points for Motherwell in the 62nd minute to take Mark McGhee's side up to third in the table. Keith Lasley's opener after eight minutes had been cancelled out by Gretna midfielder Abdul Osman in the 18th minute. Craig Barr was sent off for the home side.
Aberdeen came storming back after Merouane Zemmama fired Hibs in front in the fifth minute, with Craig Brewster grabbing a brace (18 and 37) minutes and Jamie Smith also finding the target (57) to make it 3-1. However, Steven Fletcher trimmed the lead to 3-2 after 70 minutes and Dean Shields equalised six minutes from time.
Dundee United heaped more misery on Inverness as a Sean Dillon goal in the 47th minute and two Barry Robson penalties (58 and 81) made it four defeats in a row for the Highlands club.
Walter Smith's side put seven past Falkirk last weekend but they found Killie goalkeeper Alan Combe in top form in an open first half. DaMarcus Beasley finally managed to break the deadlock seven minutes after the break as he rifled home Barry Ferguson's low cross. Danny Invincible levelled for Kilmarnock after 61 minutes with a shot into the roof of the net, after a flowing move involving long-time Rangers target Steven Naismith. However, Jean-Claude Darcheville popped up 14 minutes from time to keep Rangers top of the table.