Hearts' Ryan Stevenson then shot high and wide from the edge of the penalty area.
Ryan Stevenson forced Motherwell goalkeeper Darren Randolph into a save and Steven Saunders struck a Hearts post before half-time.
Motherwell had the first half's best chance in the 35th minute, when Chris Humphrey outpaced Ryan Stevenson and found Blackman.
Calum Elliot and then Suso were sent off the bench for Gary Glen and Ryan Stevenson respectively as Hearts pressed for parity.
Kevin Kyle converted the spot-kick on 64 minutes and Ryan Stevenson added a breakaway goal in injury time to seal the victory for Hearts.
Ryan Stevenson failed to find the target with an early chance for Hearts, while Saints' Liam Craig forced a good save from Jamie MacDonald.
Ryan Stevenson added a late strike on the counter-attack to make it three wins in the space of seven days for the Edinburgh side.
Chris Innes netted an own goal for Caley Thistle in the closing seconds of the first half then Ryan Stevenson and Calum Elliot completed the victory.
The two sides traded blows early on, with Ryan Stevenson sending a snap shot over from 15 yards and Chris Millar looping a drive just wide at the other end.
Ryan Stevenson watched a late effort sail harmlessly over the Accies bar and Calum Elliot came close in the final minute, but the third goal wasn't required as Hearts easily claimed all three points.
Eager for a turnaround in fortunes, Hearts withdrew Michael Stewart and Glen and sent on Ian Black at Calum Elliot at half-time and made a further change early in the second half with Ryan Stevenson replacing Glen.
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