Nottingham Forest came from two goals down against Birmingham to preserve their unbeaten start to the season in the Championship.
But Forest came roaring back with goals from substitutes Simon Cox and Dan Harding to stretch their unbeaten start to five games.
Harding lifted the roof of The City Ground as he bagged Forest’s equaliser four minutes from time with a cool finish from the edge of the six-yard box.
It was no more than they deserved after another plucky display that looked like yielding very little reward when Mullins and King struck.
Cox launched the fight back with a goal of exquisite quality before Harding sent the majority of the crowd of 22,738 into ecstasy with his first goal for the club.
It could have been even better for The Reds had Billy Sharp managed to direct his last-gasp header on target rather than over the bar as they laid siege on the Birmingham goal.
Boss Sean O’Driscoll made just one change to his starting line-up as he handed loan signing Sharp his full debut.
The ace marksman took the place of Cox, who was named as a substitute after recovering from the foot injury he had picked up in midweek while on international duty with the Republic of Ireland.
Sharp got his first sniff of goal after 11 minutes when England goalkeeper Jack Butland failed to hold a right-wing cross from Sam Hutchinson. The ball broke nicely for Sharp but he fired straight at the Birmingham No.1 from just inside the area.
Butland made a finger-tip save to deny Lewis McGugan an almost identical goal to the one he had bagged against Charlton a fortnight earlier.
The in-form midfielder unleashed a fiercely struck free-kick from close to the left-hand touchline that Butland dealt with at the expense of a corner.
Forest squandered a golden opportunity to break the deadlock midway through the first half after Simon Gillett had set his ex-Doncaster teammate Sharp racing clear down the right. He fed Andy Reid in the area but the move lost its momentum as the Irishman played a return ball to Sharp.
The alertness of Lee Camp denied King as the goalkeeper dashed off his line to make a superb block after the former Forest striker had been sent clear by Leroy Lita.
Butland tipped over a Reid free-kick as O’Driscoll’s men strived for an opener, while King fired over from a promising position in the closing stages of the first half.
Reid fired an inviting ball across the face of the visitors’ six-yard box as Forest made a bright start to the second half.
Sharp drew a cheer from both sets of supporters when he inadvertently sent referee Mark Halsley tumbling to the ground.
O’Driscoll made a change on the hour mark as he introduced Cox to the action at the expense of Dexter Blackstock.
But it was Birmingham who stole the initiative with two goals. Mullins fired them in front in emphatic style after King’s initial shot had been blocked by Sam Hutchinson.
And the writing looked to be on the wall for O’Driscoll’s men when King swept a shot past Camp after great work down the right by substitute Nathan Redmond.
Forest – and Cox – had other ideas as he gave his side a foothold in the game by deftly controlling a long ball forward from McGugan before lobbing Butland with his second touch.
That put Birmingham on the back foot and the home side got their reward four minutes from time when Harding popped up to beat Butland.
Bookings: Ayala 22', Hutchinson 54', Collins 75', Cox 88'
Birmingham: Butland, Murphy, Caldwell(c), Ibanez, Burke (Redmond 70'), Mullins, King, Lovendrands (Elliott 50'), Spector, Caddis, Lita (Fahey 79').
Scorers: Mullins 69', King 71'
Referee: Mark Halsey