Lowly Hamilton stunned leaders Partick 1-0 thanks to an own-goal from debutant Graeme Smith.
The former Rangers, Hibs and Motherwell goalkeeper only signed this week after an injury to regular Thistle number one Scott Fox.
But Smith's first Jags appearance turned into a nightmare five minutes before the interval when he fumbled Alister Crawford's corner into his own net.
Hamilton had their chances to take the lead before that, with Steven May blazing over from inside the area and Martin Canning seeing his header cleared by Ross Forbes.
Partick improved after the break and Steven Lawless fired a good chance over.
But their hopes evaporated when Paul Paton was sent off for a bringing down May with 15 minutes left as the Accies held on to register their first home win of the season.