Former Rangers player Andy Halliday scored a superb goal as Premiership rivals Hearts stole a surprise early march on the Gers.
Halliday was released by the Light Blues last summer and soon snapped up by the Jambos on a two-year deal.
Although he has received criticism at times, the bluenose helped the Edinburgh club to the Championship title last season and has started this campaign very well.
Hearts won all four of their League Cup group stage matches without conceding, with Halliday notching a goal and an assist against Cove Rangers, while he contributed to a shock opening day win over Celtic and then netted his second of the season at St Mirren on Saturday afternoon.
The former Ger put the visitors in front in Paisley in just the 16th minute, whipping a Liam Boyce cutback into the top right corner from the left side of the area.
Liam Boyce doubled the advantage in the 73rd minute and although Joe Shaughnessy grabbed one back for the Buddies, Hearts would emerge victorious with a 2-1 final scoreline.
Following Rangers’ slip up at Dundee United earlier in the day, it means that the Jambos are now top of the table and three points clear of the Gers.
It’s been a surprisingly strong start for the newly-promoted side with Halliday a key figure so far, but few would expect it to stay as it is for long.
The champions aren’t firing on all cylinders yet but the defeat at Tannadice may well be the jolt they needed to really get to work on their title defence.
Most Bears know that patience is required but many still took exception to a post-match comment from Steven Gerrard.