Hearts extended their unbeaten home league run this season by beating Falkirk 3-0 at Tynecastle on Wednesday (Thursday AEST), while Kelechi Iheanacho's added-time penalty snatched Celtic a 3-2 win at Motherwell.
"I think it's disgusting, I don't think it's a penalty kick," Hearts boss Derek McInnes said.
"If I'm Motherwell, I'm really disappointed with that.
"I've seen it (the replay) before I came out to speak to you and I think it's so poor that they've been given that penalty. And it looks as if they've been 'given' it.
"I think they've been very fortunate, very fortunate on that side. And we have to realise we're up against everything."
The Jambos needed victory and for Celtic to lose their penultimate match to seal their first domestic title in 66 years, but now the two sides face-off at Celtic Park on Saturday in a title decider.
Two goals in five first-half minutes put Hearts in control against Falkirk, with Frankie Kent heading them into a 29th-minute lead and Socceroos midfielder Cammy Devlin firing home from inside the penalty area.
It was the 27-year-old Sydneysider's first goal since December and his second of the season.
Blair Spittal curled home the Tynecastle side's third in the closing stages, soon after news of Motherwell's late equaliser against Celtic had filtered through the stands.
Daizen Maeda cancelled out Elliot Watt's early opener for Motherwell at Fir Park and after Benjamin Nygren had edged the visitors ahead, Liam Gordon fired a late equaliser before Iheanacho converted a penalty in the ninth minute of added time.
Hearts are bidding to become the first team to break the dominance of Celtic and Rangers in Scotland since Aberdeen in 1985.
At Ibrox, Dane Scarlett struck a late winner for Hibernian as they beat Rangers 2-1.
World Cup-bound Socceroo Martin Boyle fired Hibs into an early lead and although Rangers hit back through Thelo Aasgaard, Scarlett converted Felix Passlack's cross from close range in the 89th minute.
With AAP and AP.
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