Motherwell's come-from-behind victory on Saturday saw them remain one point behind the second-placed Aberdeen, while they are now nine points clear of their nearest rivals in third.
Midfielder Chris Erskine put Partick ahead nine minutes before the interval, but goals either aside of half-time from Keith Lasley and Lionel Ainsworth put the hosts in the lead.
Forward Kallum Higginbotham then levelled from the spot following Ainsworth's foul on Aaron Taylor-Sinclair with 24 minutes to play.
And Higginbotham appeared to have given relegation-threatened Partick all three points with his second goal in the 72nd minute.
However, there was to be a final twist in the tale as late headers from John Sutton and Stephen McManus settled an enthralling encounter and further cemented Motherwell's grip on third place.
Motherwell's lead over their rivals was stretched to nine points by virtue of Inverness Caledonian Thistle's 0-0 draw with bottom club Hearts.
That slip-up allowed Dundee United to leapfrog Inverness into fourth with a 3-2 triumph over Kilmarnock.
Highly rated winger Gary Mackay-Steven opened the scoring for the hosts after 10 minutes, only for Alexei Eremenko and Kris Boyd tilt the contest in the favour of Allan Johnston's men.
Australia defender Curtis Good – on loan from Newcastle United - levelled things up on 65 minutes though, shortly after Boyd had given Kilmarnock the lead, and midfielder John Rankin secured the win six minutes later.
A late penalty from Adam Rooney kept Aberdeen in second place as Derek McInnes' men earned a 1-0 success at St Mirren.
Irish attacker Rooney kept his composure to convert from the spot 10 minutes from time after Eric Djemba-Djemba had felled Peter Pawlett to condemn St Mirren to a third straight league defeat.
Elsewhere, first-half strikes from Sam Stanton and Tom Taiwo handed Hibernian a 2-1 victory against struggling Ross County.
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