Match ends, Valencia 0, Juventus 2.
A tearful Cristiano Ronaldo was controversially sent off as Juventus claimed a hard-fought win at Valencia.
The Portuguese forward, making his Champions League debut for Juve, appeared to grab Valencia defender Jeison Murillo's hair as they tangled off the ball midway through the first half and referee Felix Brych consulted his assistant behind the goal before showing the five-time Champions League winner a straight red card.
Ten-man Juve rallied and took the lead on the stroke of half-time when Miralem Pjanic scored from the penalty spot, and shortly after the break, the Bosnian midfielder stroked home another spot-kick.
Valencia were then awarded a penalty in stoppage time but Juve goalkeeper Wojciech Szczesny denied Daniel Parejo to preserve the Italians' clean sheet.
It was an unhappy return to Spain for Ronaldo, who moved to Juve from Real Madrid for £99.2m in the summer.
His influence on the game was growing when he tried to latch onto a cross and was blocked off by a tumbling Murillo. He gesticulated to Murillo to get up and appeared to pull the defender's hair before turning away in frustration.
Amid a hostile atmosphere, opposing players clashed in the box and the referee spoke with his assistant at length before producing a red card.
The Champions League's record goalscorer was visibly furious, protesting his innocence but finally leaving the pitch in tears.
It was his first sending off in 154 Champions League appearances and he now faces at least a one-game ban.
Juventus have won Serie A seven years in a row and they used all their experience to silence the raucous Valencia fans and close out the win.
Manager Massimo Allegri signed Ronaldo to help make the difference in this competition but they were comfortable even without their big summer signing.
They should have been ahead before Ronaldo's sending off and finally pulled in front with Pjanic's first penalty shortly before half-time after Parejo fouled Joao Cancelo in the box.
In the second half, Murillo wrestled Leonardo Bonucci to the ground from a corner and Pjanic stepped up to beat goalkeeper Neto once more.
Although Valencia were handed a penalty in injury time after late substitute Daniele Rugani fouled Gabriel, Parejo's weak effort was saved by Szczesny.
On this evidence, the Italian champions look a good bet for another strong campaign after reaching the 2016-17 final.
Their defensive resilience is unparalleled and they once again demonstrated their uncanny ability to grind out a result.
Once Ronaldo is up and running, they will be well placed to chase a first Champions League title since 1996.
Valencia face Villarreal in La Liga on Sunday (15:15 BST), before Juventus go to Serie A new boys Frosinone Calcio (19:30 BST).
Valencia visit Manchester United in their next Champions League game while a Ronaldo-less Juventus host Young Boys, with both fixtures on Tuesday, 2 October (20:00 BST).
Match ends, Valencia 0, Juventus 2.
Second Half ends, Valencia 0, Juventus 2.
Corner, Valencia. Conceded by Leonardo Bonucci.
Attempt blocked. Denis Cheryshev (Valencia) left footed shot from the left side of the box is blocked.
Penalty saved! Daniel Parejo (Valencia) fails to capitalise on this great opportunity, right footed shot saved in the bottom left corner.
Daniele Rugani (Juventus) is shown the yellow card for a bad foul.
Penalty Valencia. Gabriel draws a foul in the penalty area.
Penalty conceded by Daniele Rugani (Juventus) after a foul in the penalty area.
Corner, Valencia. Conceded by Federico Bernardeschi.
Attempt blocked. Carlos Soler (Valencia) right footed shot from outside the box is blocked. Assisted by Rodrigo Moreno.
Attempt missed. Rodrigo Moreno (Valencia) header from the centre of the box misses to the left. Assisted by Daniel Wass with a cross.
Gabriel (Valencia) wins a free kick in the defensive half.
Foul by Alex Sandro (Juventus).
Foul by Denis Cheryshev (Valencia).
Federico Bernardeschi (Juventus) wins a free kick in the defensive half.
Attempt blocked. Rodrigo Moreno (Valencia) left footed shot from outside the box is blocked. Assisted by Santi Mina.
Delay over. They are ready to continue.
Substitution, Juventus. Daniele Rugani replaces Douglas Costa because of an injury.
Delay in match Douglas Costa (Juventus) because of an injury.
Attempt saved. Douglas Costa (Juventus) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by Blaise Matuidi.
Attempt blocked. Rodrigo Moreno (Valencia) left footed shot from the centre of the box is blocked. Assisted by Denis Cheryshev with a cross.
Attempt blocked. Daniel Parejo (Valencia) right footed shot from outside the box is blocked. Assisted by Rodrigo Moreno.
Attempt missed. Kevin Gameiro (Valencia) right footed shot from the centre of the box is high and wide to the right following a corner.
Corner, Valencia. Conceded by Leonardo Bonucci.
Attempt missed. Kevin Gameiro (Valencia) right footed shot from outside the box is high and wide to the right. Assisted by Daniel Parejo.
Wojciech Szczesny (Juventus) is shown the yellow card.
Attempt missed. Carlos Soler (Valencia) right footed shot from outside the box is just a bit too high following a corner.
Corner, Valencia. Conceded by Leonardo Bonucci.
Attempt blocked. Rodrigo Moreno (Valencia) header from the centre of the box is blocked. Assisted by Daniel Parejo with a cross.
Corner, Valencia. Conceded by Leonardo Bonucci.
Attempt saved. Carlos Soler (Valencia) right footed shot from outside the box is saved in the bottom left corner. Assisted by Daniel Parejo.
Offside, Valencia. Kevin Gameiro tries a through ball, but Daniel Parejo is caught offside.
Corner, Valencia. Conceded by João Cancelo.
Corner, Valencia. Conceded by Giorgio Chiellini.
Corner, Valencia. Conceded by João Cancelo.
Giorgio Chiellini (Juventus) wins a free kick in the defensive half.
Foul by Kevin Gameiro (Valencia).
Offside, Juventus. Wojciech Szczesny tries a through ball, but Mario Mandzukic is caught offside.
Mario Mandzukic (Juventus) wins a free kick in the attacking half.
Foul by Gabriel (Valencia).