Hearts head coach Derek McInnes says his side are "up against everybody" after a "disgusting" 99th-minute penalty winner for Celtic ensured the Scottish Premiership title race would go to a final-day decider on Saturday.
With league leaders Hearts cruising to a 3-0 win over Falkirk, the concession of a late equaliser at Motherwell looked like leaving Celtic three points back before Hearts go to Glasgow on Saturday.
Replays seemed to show the ball hitting Nicholson's head, rather than his raised hand, but Beaton awarded a spot kick which Kelechi Iheanacho converted to snatch a 3-2 win.
Draw at Celtic Park will earn Hearts title after Falkirk draw
Controversial 99th-minute penalty keeps Celtic's title hopes alive
"It's disgusting. We're up against it, we're up against everybody. I don't think it's a penalty. It's so poor and it looks as though [Celtic] have been given it. They have been very fortunate."
Had Celtic dropped points, Hearts could have afforded to lose by two goals at Celtic Park on Saturday and still be crowned champions for the first time since 1960.
Now, though, they must avoid defeat if they are to become the first side outside Celtic or Rangers to win the Scottish top flight in four decades.
"It's going to the last game. We're delighted to be part of it," McInnes added.
"To do it, we're going to have to go and get a positive result. I'm looking forward to it already, there'll be no feeling sorry for ourselves. What a game it's going to be."