Ronaldo comes off bench to rescue 10-man Juve from first Serie A defeat of season
Ronaldo had been rested for the first time by boss Massimiliano Allegri since moving to Juve, but was called on with 25 minutes left to play as Juventus found themselves 2-1 down and playing with 10 men after Rodrigo Bentancur saw red for a second bookable offence.
But the prolific Portuguese restored parity when he popped up to head home from close range on 78 minutes after a Miralem Pjanic delivery into the box was headed down by Mario Mandzukic.
The goal came after Atalanta looked set for an unlikely win at the Stadio Atleti Azzurri d'Italia, putting an early Berat Djimsiti own goal behind them to take the lead through a double from Duvan Zapata.
But Ronaldo had other ideas, scoring his 12th league goal in 18 Serie A games since making the move from Real Madrid in the summer.
Juventus could even have won the game but Mandzukic failed to connect with a Ronaldo cross and Leonardo Bonucci saw an injury-time effort ruled out for offside.
The draw – which is just the second time Juve have dropped league points this season – leaves Juve sitting pretty at the top of Serie A on 50 points, nine ahead of Napoli, who have a game in hand.
Atalanta move up to eighth.