Just 29 minutes into the Champions League Group H opener against Valencia, Ronaldo appeared to make contact with Murillo's head in an off-the-ball incident.
The pair had come together with Murillo hitting the deck, and Ronaldo reaching down to make brief contact as he passed by the downed defender.
The red card was shown for the incident, leaving Ronaldo visibly distraught as he was sent off by referee Felix Brych.
The Portugal international forward first fell to the turf in disbelief, and was later seen with his face in his hands.
The moment that saw Cristiano Ronaldo see red— B/R Football (@brfootball) September 19, 2018
[🎥: U.S. only] pic.twitter.com/IB3ffZweXw
How we didn’t expect Cristiano Ronaldo’s Champions League debut for Juventus to end...— Football on BT Sport (@btsportfootball) September 19, 2018
⚪️ With a goal
⚪️ With a hat-trick
🔘 In tears
He’s received his first-ever red card in the competition 😮 pic.twitter.com/VbOqOAh07q
It was the first red card in the Champions League in Ronaldo's career, in his 154th appearance.
The expulsion, moreover, highlights Juventus' rather spotty disciplinary record in European competition.
Ronaldo's sending off was the Italians' 26th in the Champions League, the most of any team in the tournament's history.
It also marks the third consecutive European match the Old Lady have finished with 10 men, a run only equalled previously by Bordeaux in 2000 and Qarabag in 2017.
Paulo Dybala was sent off for the Turin side in the quarter-final first leg against Real Madrid last season, while Gianluigi Buffon saw red in the final minute of the decider prior to a penalty that was, ironically, converted by Ronaldo.
That also means Ronaldo will miss the next game, Juventus' home date against Young Boys, and possibly their trip to Old Trafford to face his former club Manchester United, though that will be up to UEFA's Disciplinary Body.
The UEFA regulations state: "As a rule, a player who is sent off the field of play is suspended for the next match in a UEFA club competition (i.e. UEFA Champions League, UEFA Europa League or UEFA Super Cup). In case of serious offences, the UEFA Control, Ethics and Disciplinary Body is entitled to augment this punishment, including by extending it to other competitions."
Despite being down a man, Juventus went into half-time up a goal after Dani Parejo's foul allowed Miralem Pjanic to give the Old Lady the lead from the spot just before the end of the first 45.
Then Murillo himself was flagged for a foul in the area early in the second half, which Pjanic again finished off to double Juventus' advantage.