Ronaldo was dismissed in the 29th minute for a seemingly minor clash with Valencia defender Jeison Murillo as the pair jostled in the box awaiting a cross.
Miralem Pjanic's pair of penalties gave Juve the win and they are second on goal difference in Group H behind Manchester United following their 3-0 triumph at Young Boys.
Real dominated Roma but had a nervous wait until Isco broke the deadlock on half time. Viktoria Plzen were held 2-2 by CSKA Moscow in the other Group G game.
In Group E Bayern Munich won 2-0 at Benfica after Ajax dismantled AEK Athens 3-0 but there was a major shock in Group F as Manchester City lost 2-1 at home to Lyon after Shakhtar Donetsk drew 2-2 with Hoffenheim.
Juve hope Portuguese star Ronaldo can help them over the finish line after two losing finals in the last four years but they earned this win without him.
The visitors started brightly but Ronaldo was left distraught when German referee Felix Brych consulted with the goalline official before producing the red card for an apparent pull at Murillo's hair.
"We were playing very well until Ronaldo's sending off but we continued to play our football despite that blow and deservedly scored two goals," Juve coach Massimiliano Allegri said.
"I think the lads did very well tonight, especially because they played good football when we had to do that. We all pulled together as a team when it was the moment to defend these three points."
Being a man short had little impact on Juventus and Joao Cancelo won a penalty in first half injury time chasing his own rebound off the bar. Pjanjic made no mistake and scored to the same side early in the second half after Murillo fouled Leonardo Bonucci at a set piece.
Daniel Parejo, who conceded the first spot kick, missed an injury time penalty as Valencia failed to get a consolation.
Manchester United were second best at Young Boys but a brilliant Paul Pogba drive settled them and the French World Cup winner bagged his second from the spot before Anthony Martial completed the scoring.
Real are chasing a fourth consecutive title, now under new coach Julen Lopetegui and without Ronaldo, and started in determined fashion against Roma.
They missed several chances before Isco curled home a glorious free kick at the end of the first half. Gareth Bale's fine counter-attack sealed the game just before the hour and Mariano scored in injury time.
"I thought the performance was very good tonight, the only disappointment was that we didn't score more," said Bale.
"Real Madrid will always be Real Madrid, no matter who leaves. We keep on trying to win, keep on trying to score goals."
Michael Krmencik's first half double gave Plzen an advantage over CSKA but Fedor Chalov and Nikola Vlasic's late penalty rescued a point.
Manchester City are a major favourite in the tournament but were out of sorts against Lyon, who punished their sloppy mistakes in front of a flat crowd.
Maxwel Cornet put the guests in front after Fabian Delph missed a cross and Nabil Fekir converted a counter-attack after the guests won the ball in midfield.
Bernardo Silva pulled one back in the second half but they couldn't find an equalizer.
"We have to focus on a poor first half when we weren't at our best," Silva told BT Sport. "We didn't play with our usual intensity. We were not good enough tonight."
Hoffenheim were denied a victory in their first-ever Champions League group stage game away to Shakhtar Donetsk as the hosts snatched a 2-2 in Kharkiv.
Florian Grillitsch, in just six minutes, and Haavard Nordtveit scored for the Bundesliga side but Ismaily and Maycon late on equalized twice to ensure a share of the spoils.
Bayern triumphed in Lisbon on Niko Kovac's Champions League debut as coach with Robert Lewandowski and Renato Sanches, on his return to his former club, striking the goals.
"I'm pleased for Renato and us as a team," Kovac said. "What he has done in the pre-season was extraordinary."
Ajax sit first in Group E, thanks to a double from Nicolas Tagliafico either side of Donny van de Beek netting against AEK.
Miralem Pjanic's pair of penalties gave Juve the win and they are second on goal difference in Group H behind Manchester United following their 3-0 triumph at Young Boys.
Real dominated Roma but had a nervous wait until Isco broke the deadlock on half time. Viktoria Plzen were held 2-2 by CSKA Moscow in the other Group G game.
In Group E Bayern Munich won 2-0 at Benfica after Ajax dismantled AEK Athens 3-0 but there was a major shock in Group F as Manchester City lost 2-1 at home to Lyon after Shakhtar Donetsk drew 2-2 with Hoffenheim.
Juve hope Portuguese star Ronaldo can help them over the finish line after two losing finals in the last four years but they earned this win without him.
The visitors started brightly but Ronaldo was left distraught when German referee Felix Brych consulted with the goalline official before producing the red card for an apparent pull at Murillo's hair.
"We were playing very well until Ronaldo's sending off but we continued to play our football despite that blow and deservedly scored two goals," Juve coach Massimiliano Allegri said.
"I think the lads did very well tonight, especially because they played good football when we had to do that. We all pulled together as a team when it was the moment to defend these three points."
Being a man short had little impact on Juventus and Joao Cancelo won a penalty in first half injury time chasing his own rebound off the bar. Pjanjic made no mistake and scored to the same side early in the second half after Murillo fouled Leonardo Bonucci at a set piece.
Daniel Parejo, who conceded the first spot kick, missed an injury time penalty as Valencia failed to get a consolation.
Manchester United were second best at Young Boys but a brilliant Paul Pogba drive settled them and the French World Cup winner bagged his second from the spot before Anthony Martial completed the scoring.
Real are chasing a fourth consecutive title, now under new coach Julen Lopetegui and without Ronaldo, and started in determined fashion against Roma.
They missed several chances before Isco curled home a glorious free kick at the end of the first half. Gareth Bale's fine counter-attack sealed the game just before the hour and Mariano scored in injury time.
"I thought the performance was very good tonight, the only disappointment was that we didn't score more," said Bale.
"Real Madrid will always be Real Madrid, no matter who leaves. We keep on trying to win, keep on trying to score goals."
Michael Krmencik's first half double gave Plzen an advantage over CSKA but Fedor Chalov and Nikola Vlasic's late penalty rescued a point.
Manchester City are a major favourite in the tournament but were out of sorts against Lyon, who punished their sloppy mistakes in front of a flat crowd.
Maxwel Cornet put the guests in front after Fabian Delph missed a cross and Nabil Fekir converted a counter-attack after the guests won the ball in midfield.
Bernardo Silva pulled one back in the second half but they couldn't find an equalizer.
"We have to focus on a poor first half when we weren't at our best," Silva told BT Sport. "We didn't play with our usual intensity. We were not good enough tonight."
Hoffenheim were denied a victory in their first-ever Champions League group stage game away to Shakhtar Donetsk as the hosts snatched a 2-2 in Kharkiv.
Florian Grillitsch, in just six minutes, and Haavard Nordtveit scored for the Bundesliga side but Ismaily and Maycon late on equalized twice to ensure a share of the spoils.
Bayern triumphed in Lisbon on Niko Kovac's Champions League debut as coach with Robert Lewandowski and Renato Sanches, on his return to his former club, striking the goals.
"I'm pleased for Renato and us as a team," Kovac said. "What he has done in the pre-season was extraordinary."
Ajax sit first in Group E, thanks to a double from Nicolas Tagliafico either side of Donny van de Beek netting against AEK.