Title-chasing Fiorentina spurned the chance to go top of Serie A after a 1-1 draw at Sassuolo on Monday pushed Paulo Sousa's men up to second one point behind leaders Inter Milan.
Fiorentina travelled to the Mapei Stadium looking to go clear of Inter ahead of the Nerazzurri's later match at Napoli on Monday.
But after Borja Valero capped a lightning start by the visitors to break the deadlock on five minutes, Fiorentina were made to pay for a series of later misses when Sergio Floccari headed home the leveller three minutes before the interval.
Sassuolo have made such a positive start this season that coach Eusebio Di Francesco has been mentioned in reports speculating on who could replace crisis-hit Roma coach Rudi Garcia in the event of his sacking.
But the hosts were under the cosh from the off after a lightning Fiorentina start that produced two penalty claims in the opening four minutes.
Federico Bernardeschi's volley from a Borja Valero free-kick appeared to hit the arm of Sime Vrsaljko and after Valero almost caught Andrea Consigli out with an inswinging corner the 'keeper had to bat away, Josip Ilicic tumbled to the turf when impeded by Acerbi in the area.
Both claims were waved away but Fiorentina made good barely a minute later when Ilicic capitalised on chaotic defending to set up the unmarked Valero who, via a touch from Giuseppe Rossi, had time to pick his spot from eight yards.
Sassuolo looked all at sea and endured a nervous moment when Consigli was left out of his goal after a wayward clearance that Valero promptly collected. The Spaniard, who is reportedly being scouted by
Manchester United, saw his strike head for home but Consigli scrambled back to block in time.
It was stirring stuff from the visitors, and Consigli produced a great stop to thwart Ilicic on a one-on-one when the Slovenian playmaker was sent through on the right of goal.
But Fiorentina were made to pay for those misses three minutres before the interval when Floccari rose on the edge of the six-yard box to fire a bullet header through Ciprian Tatarusanu's hands.
With nine league goals so far including a brace last week when he came off the bench to level 2-2 at home to Empoli, Nikola Kalinic's entry was only a matter of time and 11 minutes into the second half he replaced Rossi.
Fiorentina came close when Manuel Pasqual burst down the left and controlled a long midfield pass to unleash an angled drive that Consigli parried for a corner.
But Sassuolo remained a threat and had a great chance when Vrsaljko fired an inviting cross to Floccari, only for Gonzalo Rodriguez to rush back and fire out for a corner.
Fiorentina pressed in the closing minutes and were unlucky when claiming a third penalty award after Valero's attempted cutback struck a Sassuolo arm.