It took the Portuguese forward almost 320 minutes to score his first league goal for Juve and he did it with the simplest of tap-ins.
His second was a more typical Ronaldo finish - a driven effort across the goalkeeper - and the 33-year-old took to Twitter to share the joy of finally breaking his Juve duck.
The Brazilian was red-carded and will probably face a lengthy ban after spitting into the face of Sassuolo's Frederico Di Francesco.
In one of the most revolting scenes imaginable on a field of play, Costa leaned right in and gobbed into Di Francesco's mouth.
Juventus won the game thanks to a brace from Cristiano Ronaldo, but Costa's actions have cast a dark shadow over the victory. "Obviously I'm happy to score my first goals, I was looking forward to it", he said.
Ronaldo could have completed a hat-trick late on but missed two easy chances from inside the penalty area.
Eliud Kipchoge smashes marathon world record in Berlin
I also congratulate his compatriots Amos Kipruto & Wilson Kipsang for going out valiantly to bring a 1-2-3 victory for #TeamKenya. Kipchoge ended up running 2:00:25 but the time is not world record eligible due to the pacing strategy alterations.
He volleyed wide from an unmarked position six metres out and failed to hit the target when the rebound landed at his feet as Joao Cancelo's shot was saved by Consigli.
In fact, the only active player who joins the superstar duo on this prolific scoring list of having scored over 500 career goals is Zlatan Ibrahimovic.
Both sides have made ideal starts to their domestic campaigns with five wins, PSG thrashing St Etienne 4-0 at home on Friday and Liverpool enjoying a convincing 2-1 victory at Tottenham Hotspur.
But Chievo, beaten 6-1 by Fiorentina last time out and on minus points after being deducted three points by the Italian football federation for false accounting, battled back in the second half.
La Liga: Valencia 0 drew with Real Betis 0; Athletic Bilbao 1 (Muniain 32) drew with Real Madrid 1 (Isco 63).